Apparatus and method for controlling a wireless network

ABSTRACT

A wireless network, connecting network users to a communications network, comprises base stations connected to the communications network and terminals connected to the network users, each terminal having a link with a base station to form a base station/terminal pair, the links established over a wireless resource comprising resource blocks. The method comprises: determining, for each base station/terminal pair, a set of resource utilization fractions; determining a set of co-channel interference matrices for each network component, distributing, to each base station, corresponding elements from the sets of resource utilization fractions and the sets of co-channel interference matrices; suppressing, in each network component, co-channel interference in dependence on the determined co-channel interference matrix; and dynamically establishing links required to handle the network traffic for each base station by selecting from the resource blocks in accordance with the resource utilization fractions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for controllinga wireless feeder network used to couple access base stations of anaccess network with a communications network.

2. Description of the Prior Art

Typical access networks provide a plurality of access base stationswhich communicate via wireless links with mobile or fixed end userequipment. A number of wireless communications protocols are known forthe communications between the access base stations and the end userequipment, for example WiFi, WiMAX, or LTE wireless communications, etc.

The various access base stations need to be coupled with acommunications network to allow traffic originating from the userequipment to be propagated on to the communications network, and fortraffic within the communications network to be delivered to therequired end user equipment within the access network. One known way toprovide such connection between the communications network and theaccess network is to provide wired backhaul connections from each of thebase stations to the communications network. However, this requires theaccess base stations to be located in places where it is feasible toprovide a wired backhaul connection to those access base stations. As analternative to a wired backhaul, it is also known to provide a dedicatedout-of-band wireless backhaul to provide a point-to-point wirelessconnection between each base station and the communications network.

However, as the demands for bandwidth increase, cell splittingtechniques have been used, where a cell that would have previously beenserviced by a single access base station is sub-divided into smallergeographical regions served by additional access base stations, suchcell splitting techniques providing a well-proven technology forincreasing system capacity. However, as the number of access basestations are increased, this increases the cost of providing theearlier-described wired or wireless point-to-point backhaul connectionsbetween the various access base stations and the communications network.This significantly increases the cost to the operator. For wiredbackhaul, the cost clearly increases as each additional backhaulconnection is required. For a wireless backhaul solution, there is asimilar increase in the cost, since scarce radio frequencies must beallocated in advance, and once fixed the frequencies allocated foraccess (from an access base station to the mobile or fixed end userequipment and vice versa) and for the backhaul (from a base station tothe network router and vice versa) cannot change.

There is a growing requirement for the access base stations to be madesmaller and easier to deploy in a variety of locations. For example itwould be desirable to be able to place such access base stations onstreet furniture such as lampposts and signage. However, to achieve suchan aim, it is necessary for the access base stations to be small,compact and consume low power. There is also a need for an efficient wayto connect such access base stations to the communications network via awireless backhaul connection.

One known approach for reducing the costs associated with providing abackhaul connection for the various base stations is to employ one ormore of the base stations as relay stations. Hence, in such embodiments,relay traffic can be passed between base stations, so that at least someof the base stations do not directly need to be connected to thebackhaul. However, such relay traffic consumes a significant amount ofthe total resource provided within the access network for handling datatraffic.

Accordingly, it would be desirable to provide an improved mechanism forcoupling access base stations of an access network with a communicationsnetwork, which allows freedom in placement of base stations of theaccess network, whilst providing a spectrally efficient backhaulconnection.

SUMMARY OF THE INVENTION

Viewed from a first aspect, the present invention provides a method ofcontrolling a wireless network for connecting network users to acommunications network, the wireless network comprising a plurality ofnetwork components, the network components comprising a plurality ofbase stations connected to the communications network and a plurality ofterminals connected to the network users, each terminal having a linkwith a base station to form a base station/terminal pair, and the linksbeing established over a wireless resource comprising a plurality ofresource blocks, the method comprising the steps of:

determining, for each base station/terminal pair, a set of resourceutilisation fractions, said set of resource utilisation fractionsindicating probabilities for establishing said link between that basestation and that terminal via each of said plurality of resource blocks;

determining a set of co-channel interference matrices, a co-channelinterference matrix being determined for each network component, saidco-channel interference matrix indicative of an expected interferencefrom other network components, for each of said plurality of resourceblocks, when that network component receives network traffic via thatresource block, wherein said expected interference is probabilisticallydetermined in dependence on said sets of resource utilisation fractions;

distributing, to each base station, corresponding elements from saidsets of resource utilisation fractions and from said sets of co-channelinterference matrices;

suppressing, in each network component, co-channel interference independence on the co-channel interference matrix determined for thatnetwork component; and

in each base station, when exchanging network traffic with saidplurality of terminals, dynamically establishing said links as requiredto handle said network traffic for that base station by selecting fromsaid resource blocks in accordance with said resource utilisationfractions.

In accordance with the present invention, a wireless network is providedcomprising a plurality of network components for connecting networkusers to a communications network. These network components comprise aplurality of base stations coupled to the communications network and aplurality of terminals connected to the network users, each terminalhaving a link with a base station to form a base station/terminal pair.Further, the links are established over a wireless resource comprising aplurality of resource blocks.

The resource blocks form a plurality of orthogonal resources which canbe used to provide the links. These orthogonal resources can be providedin a variety of ways. For example, in accordance with a “Time DivisionMultiple Access” (TDMA) approach, a particular frequency channel of thewireless resource can be partitioned in the time domain such that eachresource block occupies a different time slot. As another example, in a“Frequency Division Multiple Access” (FDMA) approach, a band offrequencies may be partitioned, so that each individual frequency formsa resource block. In a combined TDMA/FDMA approach, a combination oftime/frequency slot can be used to define each resource block.

As another example, in a “Code Division Multiple Access” (CDMA)approach, a particular frequency channel may be partitioned by applyingdifferent orthogonal codes to thereby establish a plurality of resourceblocks within the frequency channel.

Whichever approach is taken, when controlling the wireless network it isnecessary to allocate the various resource blocks to particular links.In order to increase the system throughput, the individual resourceblocks can be reused for multiple links at the cost of increasedinterference between those links. Interference may be reduced byemploying well established reuse plans, but such schemes are generallynot adaptive, or are overly conservative, and hence do not permit themaximum utilisation of the wireless network in which they are deployed.

However, in accordance with the present invention, a set of resourceutilisation fractions are determined for each base station/terminalpair, the set of resource utilisation fractions indicating probabilitiesfor establishing the link between that base station and that terminal byeach of the plurality of resource blocks. In other words, for each linkthat is required to be established between the base station and theterminal, a probability is associated with each of the resource blocksindicating the probability of that resource block being used toestablish that link. Conversely, viewed in terms of the plurality ofresource blocks, each resource block may be allocated a probabilityassociated with one or more links, indicating the probability of thatresource block being used to establish that link. Hence rather than aparticular resource block to be used to establish a link for a basestation/terminal pair being preordained, the final selection of whichresource block is used to establish a given link is onlyprobabilistically predetermined, with one or more resource blocks beingcandidates for establishing that link, in accordance with theirallocated resource utilisation fractions.

Further, a co-channel interference matrix is then determined for eachnetwork component indicative of an expected interference from othernetwork components when that network component is receiving networktraffic using a given resource block. Hence, the co-channel interferencematrices are determined for all relevant combinations of networkcomponents and resource blocks. The expected co-channel interferencefrom the other network components is probabilistically determined independence on the sets of resource utilisation fractions. In otherwords, rather than a given co-channel interference matrix beingdetermined on the basis of a fixed knowledge of which other networkcomponents will be simultaneously using a particular resource block, asummation of expected co-channel interference for a given resource blockis performed which incorporates the probabilities that each basestation/terminal pair which is able to use that resource block will infact be doing so.

Once determined, the relevant set of resource utilisation fractions andco-channel interference matrices are distributed to each base station.The co-channel interference matrix determined for each network componentis then used to suppress that co-channel interference. For example,known transmission and/or reception beam shaping techniques may beemployed. Most significantly, each base station is then able toautonomously determine its own scheduling, i.e. how the availableresource blocks are allocated for the links that are to be establishedfor that base station, in dependence on the requirements imposed bycurrent network traffic conditions. The determination of a set ofresource utilisation fractions provides a mechanism by which each basestation has the autonomy to determine how to schedule its own traffic,but wherein overall limitations are imposed network-wide which enablenetwork-wide co-channel interference to be managed. This provides aflexible scheduling configuration for each base station giving theability to respond very quickly to instantaneous traffic bandwidthfluctuations, whilst ensuring that network-wide a high spectralefficiency is maintained.

Various techniques may be employed when dynamically establishing thelinks in each base station in accordance with the allocated resourceutilisation fractions. For example, in a preferred embodiment, saiddynamically establishing said links comprises selecting from saidresource blocks according to probabilities given by said resourceutilisation fractions. Hence the resource utilisation fractions are usedas a selection probability when selecting between the resource blocks,which enables a weighted usage of the resource blocks to be achieved.

In another embodiment said dynamically establishing said links comprisesselecting from said resource blocks such that within a predeterminedtime period usage of said resource blocks corresponds to said resourceutilisation fractions. Thus the allocation of the resource blocks for agiven link may be performed in a simple round robin fashion, but whereinthe resource blocks available for each selection is determined by theneed to comply with the resource utilisation fractions in thepredetermined time period. For example, to provide a given link anyappropriate resource block may be initially selected, but as thepredetermined time period elapses, the resource blocks available may bebiased such that usage of resource blocks evolves towards the resourceutilisation fractions.

In some embodiments, the method further comprises the step, prior tosaid step of determining, for each base station/terminal pair, said setof resource utilisation fractions, of: determining a metric for eachlink, said metric indicative of a current quality of that link, andwherein said sets of resource utilisation fractions are determined independence on said metrics. This enables the quality of each link to beinfluenced by the determination of the resource utilisation fractions.For example, the quality of a particular link (or links) could bepurposively enhanced, or alternatively a substantially equivalentnetwork-wide quality could be pursued.

The particular metric used may take a number for forms. In oneembodiment, said metric comprises a packet loss measurement. In anotherembodiment, said metric comprises a packet delay measurement. In yetanother embodiment, said metric comprises a link throughput measurement.

Depending on the particular network requirements, the determined metricfor each link may be taken into account in different ways. However inone embodiment said step of determining, for each base station/terminalpair, a set of resource utilisation fractions comprises adjusting saidresource utilisation fractions to reduce a difference between saidmetric determined and a target metric for each link. Thus, thedetermination of the resource utilisation fractions enables the networkto be controlled such that differences in the determined metrics and thetarget (or desired) metrics for each link are equalled out.

Various techniques may be employed to perform the suppression ofco-channel interference at each network component. In one embodimentsaid suppressing co-channel interference comprises arranging a beampattern at that network component to suppress the co-channelinterference during reception. For example, a multiple element antennamay be arranged to have a significant null in its beam pattern orientedtowards a source of known co-channel interference to reduce itsinterference effect. A multiple element antenna may be arranged tostrongly receive in a particular direction, whilst allowing only weakerreception in other directions. Thus in some embodiments, saidsuppressing co-channel interference comprises applying beam weights to amulti-element antenna.

Information from a number of different sources may be taken into accountwhen determining the resource utilisation fractions. In one embodiment,the method further comprises the step, prior to said step ofdetermining, for each base station/terminal pair, said set of resourceutilisation fractions, of: receiving traffic reports from the wirelessnetwork, said traffic reports indicative of previous usage of saidlinks, and wherein said sets of resource utilisation fractions aredetermined in dependence on said traffic reports. The reception oftraffic reports from the wireless network gives an indication of whattraffic is being routed where in the network and therefore enables theresource utilisation fractions to be adjusted accordingly, for exampleproviding greater bandwidth where it is currently required.

In another embodiment, the method further comprises the step, prior tosaid step of determining, for each base station/terminal pair, said setof resource utilisation fractions, of: receiving sounding data from thewireless network, said sounding data indicative of visibility betweensaid network components, and wherein said sets of co-channelinterference matrices are determined in dependence on said soundingdata. Sounding data from the wireless network can enable more accurateand up-to-date co-channel interference matrices to be determined.

In another embodiment, the method further comprises the step, prior tosaid step of determining, for each base station/terminal pair, said setof resource utilisation fractions, of: receiving expected trafficinformation, said expected traffic information indicative of anexpectation of usage of said links, and wherein said sets of resourceutilisation fractions are determined in dependence on said expectedtraffic information. For example expected traffic information may simplybe based on a recent traffic report, the expectation being that networktraffic in the near future will be similar to the near past.Alternatively the expected traffic information may take into accounthistorical traffic reports, say from a similar time of day on a previousday. For example a particular geographical area of a network (such as arailway station) may experience predictable upsurges in network activityat particular times of day (such as during the rush hours). The sourceof expected traffic information may also take other forms, such as froma network administrator who knows in advance that a particular event islikely to cause particular elements of the network to experienceunusually high traffic.

The wireless network may take a number of forms, but in one embodimentthe wireless network is a wireless feeder network, said plurality ofbase stations comprises a plurality of feeder base stations and saidplurality of terminals comprises a plurality of feeder terminals. Awireless feeder network connecting feeder base stations to feederterminals can derive particular benefit from the spectral efficiencygains provided by the present invention, due to the expense and limitedavailability of the radio frequencies available for the provision ofsuch wireless feeder networks.

The resource blocks can be formed in a number of ways. However in oneembodiment the resource blocks are formed by dividing the wirelessresource in both the frequency and time domains.

In one embodiment said base stations and terminals are at fixedlocations. This enables significant improvements in spectral efficiency,since the communications taking place over a given link do not have totake into account the further complexities involved when one or both ofthe base station and terminal are mobile.

Viewed from a second aspect, the present invention provides a wirelessnetwork controller for controlling a wireless network which connectsnetwork users to a communications network, the wireless networkcomprising a plurality of network components, the network componentscomprising a plurality of base stations connected to the communicationsnetwork and a plurality of terminals connected to the network users,each terminal having a link with a base station to form a basestation/terminal pair, and the links being established over a wirelessresource comprising a plurality of resource blocks, the wireless networkcontroller comprising:

a resource utilisation fraction computation circuitry for determining,for each base station/terminal pair, a set of resource utilisationfractions, said set of resource utilisation fractions indicatingprobabilities for establishing said link between that base station andthat terminal via each of said plurality of resource blocks;

co-channel interference matrix computation circuitry for determining aset of co-channel interference matrices, a co-channel interferencematrix being determined for each network component, said co-channelinterference matrix indicative of an expected interference from othernetwork components, for each of said plurality of resource blocks, whenthat network component receives network traffic via that resource block,wherein said expected interference is probabilistically determined independence on said sets of resource utilisation fractions; and

a distribution interface for distributing, to each base station,corresponding elements from said sets of resource utilisation fractionsand from said sets of co-channel interference matrices,

wherein said co-channel interference matrix computation circuitry isconfigured to determine said co-channel interference matrices to causethe suppression, in each network component, of co-channel interferencein dependence on the co-channel interference matrix determined for thatnetwork component,

and wherein said resource utilisation fraction computation circuitry isconfigured to determine said resource utilisation fractions such that,in each base station, when exchanging network traffic with saidplurality of terminals, said links are dynamically establishing asrequired to handle said network traffic for that base station byselecting from said resource blocks in accordance with said resourceutilisation fractions.

Viewed from a third aspect, the present invention provides a wirelessnetwork controller for controlling a wireless network which connectsnetwork users to a communications network, the wireless networkcomprising a plurality of network components, the network componentscomprising a plurality of base stations connected to the communicationsnetwork and a plurality of terminals connected to the network users,each terminal having a link with a base station to form a basestation/terminal pair, and the links being established over a wirelessresource comprising a plurality of resource blocks, the wireless networkcontroller comprising:

resource utilisation fraction computation means for determining, foreach base station/terminal pair, a set of resource utilisationfractions, said set of resource utilisation fractions indicatingprobabilities for establishing said link between that base station andthat terminal via each of said plurality of resource blocks;

co-channel interference matrix computation means for determining a setof co-channel interference matrices, a co-channel interference matrixbeing determined for each network component, said co-channelinterference matrix indicative of an expected interference from othernetwork components, for each of said plurality of resource blocks, whenthat network component receives network traffic via that resource block,wherein said expected interference is probabilistically determined independence on said sets of resource utilisation fractions; and

a distribution interface means for distributing, to each base station,corresponding elements from said sets of resource utilisation fractionsand from said sets of co-channel interference matrices,

wherein said co-channel interference matrix computation means isconfigured to determine said co-channel interference matrices to causethe suppression, in each network component, of co-channel interferencein dependence on the co-channel interference matrix determined for thatnetwork component,

and wherein said resource utilisation fraction computation means isconfigured to determine said resource utilisation fractions such that,in each base station, when exchanging network traffic with saidplurality of terminals, said links are dynamically establishing asrequired to handle said network traffic for that base station byselecting from said resource blocks in accordance with said resourceutilisation fractions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described further, by way, of exampleonly, with reference to embodiments thereof as illustrated in theaccompanying drawings, in which:

FIG. 1 is a diagram schematically illustrating a network architectureincluding a wireless feeder network in accordance with one embodiment;

FIGS. 2A and 2B schematically illustrate known wireless access networks;

FIG. 3 schematically illustrates how a wireless feeder network ofembodiments can be used to reduce the backhaul requirements of awireless access network in accordance with one embodiment;

FIG. 4 is a diagram schematically illustrating the use of a sectoredwireless feeder network in accordance with one embodiment;

FIG. 5A schematically illustrates how each feeder base station of thewireless feeder network of one embodiment has associated controllabilityregions;

FIG. 5B schematically illustrates how each feeder base station of thewireless feeder network of one embodiment has associated visibilityregions;

FIG. 6 is a flow diagram schematically illustrating a process in whichfirst a global sounding procedure is performed followed by furthersounding procedures as required in accordance with one embodiment;

FIG. 7 is a block diagram schematically illustrating the componentsprovided in a feeder network controller is accordance with oneembodiment;

FIG. 8 illustrates a set of feeder base stations and feeder terminalswhen a new wireless feeder network is being set up, and a correspondingglobal sounding schedule, according to one embodiment;

FIG. 9 is a flow diagram illustrating the basic steps performed whencarrying out a global sounding procedure in accordance with oneembodiment;

FIG. 10 is a flow diagram schematically illustrating the basic stepsperformed when carrying out downlink sounding in accordance with oneembodiment;

FIG. 11 is a flow diagram schematically illustrating the basic stepsperformed when carrying out uplink sounding in accordance with oneembodiment;

FIG. 12 schematically illustrates the visibility regions and acorresponding visibility matrix derived from a global sounding procedurein accordance with one embodiment;

FIG. 13 illustrates the network shown in FIG. 12 after the addition of afeeder base station, and a corresponding initial sounding schedule andvisibility matrix in accordance with one embodiment;

FIG. 14 is a flow diagram illustrating the basic steps performed when aninitial sounding process is carried out in accordance with oneembodiment;

FIG. 15 illustrates the updated visibility regions and visibility matrixfor the example network of FIG. 13 after the initial sounding procedurehas been carried out;

FIG. 16 illustrates the hypothesised visibility regions, an initialsounding schedule and a hypothesised visibility matrix after theaddition of a feeder terminal to the example network shown in FIG. 15;

FIG. 17 illustrates the updated visibility regions and visibility matrixof the example network of FIG. 16, after the initial sounding procedurehas been performed;

FIG. 18 is a flow diagram illustrating the basic steps performed whendetermining a periodic sounding schedule and carrying out that periodicsounding according to one embodiment;

FIG. 19 is a flow diagram illustrating the process performed at step 404of FIG. 18 according to one embodiment;

FIG. 20 is a flow diagram illustrating the process performed at step 406of FIG. 18 according to one embodiment;

FIG. 21 is a flow diagram illustrating the process performed at step 410of FIG. 18 according to one embodiment;

FIG. 22 is a flow diagram illustrating the process performed at step 412of FIG. 18 according to one embodiment;

FIG. 23 illustrates how the resource blocks of a wireless resource maybe utilised to produce a global schedule for allocating to each feederlink at least one resource block;

FIG. 24 illustrates how resource blocks may be re-used to support aplurality of feeder links;

FIG. 25 is a flow diagram schematically illustrating a process performedto compute an initial global schedule and to then iteratively modify theglobal schedule using an evolutionary algorithm, in accordance with oneembodiment;

FIG. 26 is a flow diagram illustrating the basic steps performed by theevolutionary algorithm applied at step 685 of FIG. 25;

FIG. 27 is a block diagram schematically illustrating the componentsprovided within a feeder network controller in accordance with oneembodiment;

FIG. 28 is a flow diagram illustrating how an evolutionary algorithm isused in one embodiment to generate and apply global schedules;

FIG. 29 is a flow diagram illustrating the process performed at step 810of FIG. 28 in accordance with one embodiment;

FIG. 30 is a flow diagram illustrating the process performed at step 815of FIG. 28 in accordance with one embodiment;

FIGS. 31A and 31B schematically illustrate reward functions that may beutilised when evaluating the set of hypotheses at step 820 of FIG. 28 inaccordance with one embodiment;

FIG. 32 is a flow diagram illustrating the process performed at step 820of FIG. 28 in accordance with one embodiment;

FIG. 33 is a flow diagram illustrating the process performed at step 825of FIG. 28 in accordance with one embodiment;

FIG. 34 is a flow diagram illustrating the process performed at step 835of FIG. 28 in accordance with one embodiment;

FIG. 35 is a flow diagram illustrating the process performed at step 830of FIG. 28 in accordance with one embodiment;

FIGS. 36A and 36B illustrate the same arrangement of feeder basestations and feeder terminals as shown in FIGS. 5A and 5B, but considera situation where three feeder network controllers are used tocollectively control the wireless feeder network in accordance with oneembodiment;

FIG. 37 illustrates how the process of FIG. 28 can be applied inparallel across multiple feeder network controllers in accordance withone embodiment;

FIG. 38 illustrates the steps performed at step 1230 and at step 1330 ofFIG. 37 in accordance with one embodiment;

FIG. 39 is a flow diagram schematically illustrating a process performedto compute an autonomous schedule in accordance with one embodiment;

FIG. 40 is a block diagram schematically illustrating the componentsprovided in a feeder network controller is accordance with oneembodiment;

FIG. 41 schematically illustrates co-channel interference betweennetwork components in one embodiment; and

FIG. 42 schematically shows in one embodiment the subdivision of awireless resource into a plurality of resource blocks, where eachresource block has allocated resource utilisation fractionscorresponding to the links that may be established using that resourceblock.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a block diagram schematically illustrating a networkarchitecture including a wireless feeder network in accordance with oneembodiment. As shown in FIG. 1, a number of access base stations 30, 55,80 are provided in the conventional manner to communicate via a wirelessair interface 90 with a number of mobile stations/items of end userequipment 40, 60, 85. Whilst for simplicity, each base station 30, 55,80 is shown as communicating with a single item of end user equipment,it will be appreciated that in practice such base stations formpoint-to-multipoint devices enabling a plurality of items of end userequipment to communicate with an individual base station. The items ofend user equipment may be mobile or fixed, and any one of a number ofknown wireless communication protocols may be used to effect thewireless links 90. For example, in one embodiment such wireless linksmay be constructed using WiMAX or LTE air interfaces.

The access network consisting of the various base stations 30, 55, 80and items of end user equipment 40, 60, 85 are typically connected via acommunications infrastructure 15 with an access services network gateway10 to enable inbound communication to be forwarded to the items of enduser equipment and for outbound communication to be routed to some othernetwork via the access services network gateway 10. This requires eachbase station to be provided with a backhaul connection to thecommunications infrastructure 15. The base station 30 is shown providedwith a traditional wired backhaul connection 32 to the communicationsinfrastructure 15. However, in accordance with embodiments, other basestations 55, 80 can be coupled to the communications infrastructure 15via a wireless feeder network consisting of a plurality of feeder basestations 35 coupled to the communications infrastructure 15, and aplurality of feeder terminals 50, 75 coupled to associated access basestations. The feeder base stations 35 and feeder terminals 50, 75communicate via a feeder air interface 95. Each feeder base station(FBS) forms a wireless point-to-multipoint hub which providesconnectivity between a wired infrastructure and remote sites 45, 70.Each feeder terminal provides the feeder end-point functionality.Accordingly, it terminates the feeder wireless link and, in the firstinstance, provides an interface to one or more co-located access basestations. Whilst the locations in which the feeder base stations andfeeder terminals are located may be varied, in one example the feederbase stations will typically be installed on a tower or buildingroof-top whilst the feeder terminals will typically be installed eitherbelow the roof-line, on a building, or on street furniture, such as alamp post or utility pole.

In accordance with the architecture illustrated in FIG. 1, a number ofbase sites and a number of remote sites are established. A base site 25receives a wired backhaul connection 32, 34 and in the example base site25 illustrated in FIG. 1, the base site includes not only a feeder basestation 35 but also an access base station 30 of the access network.However, in some embodiments a base site may only include a feeder basestation 35 and no access base station.

Each remote site 45, 70 includes a feeder terminal 50, 75 and anassociated access base station 55, 80. In one embodiment, the feederterminal and associated access base station are physically separatedevices, and may be coupled to each other via a variety of connections,for example an Ethernet connection such as shown in FIG. 1. In analternative embodiment, the feeder terminal and access base station maybe incorporated into a single unit used to form a remote site.

As will be described in more detail later, the wireless feeder networkprovides a wireless backhaul solution via the associated feeder airinterface 95 that partitions the resource blocks of the wirelessresource used to implement the feeder air interface 95 in a way thatensures high spectral efficiency. By achieving high spectral efficiency,it is ensured that more bandwidth is available for the actual transferof useful traffic through the access network. In one embodiment, thefeeder air interface is adaptive, in that the allocation of the resourceblocks amongst the various feeder links connecting individual feederterminals with an associated feeder base station is altered during use,for example to take account of different traffic conditions, therebyensuring that high spectral efficiency is maintained in the presence ofvarying operating conditions.

In one embodiment, one or more feeder network controllers 20 are used tocontrol the wireless feeder network with the aim of ensuring that highspectral efficiency is maintained. The dotted line 98 in FIG. 1illustrates this logical control of the feeder network controller 20over the various elements of the wireless feeder network. In practice,the control messages are routed to the various feeder base stations 35and feeder terminals 50, 75 via the wired backhaul connections 22, 34and the feeder links provided by the feeder air interface 95. The feedernetwork controller is responsible for configuring the wireless feedernetwork, monitoring its performance in use, and continually optimisingits configuration.

Optionally, the wireless feeder network may include one or more feederterminal relays 65. The feeder terminal relay is a stand alone node, thefunction of which is to receive and re-transmit feeder transport. Hence,in the example illustrated in FIG. 1, a feeder terminal relay 65 is usedto enable the feeder base station 35 to communicate with the feederterminal 75, and vice versa.

FIGS. 2A and 2B illustrate how traditional wireless access networks aresectored. In particular, FIG. 2A illustrates a macro base stationwireless access network where tri-sector access base station sites 110are used to provide communication within associated geographicalregions. Each access base station site is connected via a wired backhaulconnection 105 with a wired network 100.

Cell splitting, where a cell is sub-divided into smaller geographicalregions served by additional base stations, is a well-proven technologythat increases system capacity. Accordingly, where increased systemcapacity is required, the macro base station wireless access network maybe modified as shown in FIG. 2B to provide a pico base station wirelessaccess network. As will be appreciated from a comparison of FIG. 2B withFIG. 2A, the basic set up is the same, but each access base station site110 serves a smaller geographical region. Accordingly, it will be seenthat there is an associated increase in the backhaul requirement tosupport the various wired backhaul connections 105 to the wired network100.

FIG. 3 schematically illustrates how a wireless feeder network inaccordance with one embodiment may be used to implement a system similarto the pico base station wireless access network of FIG. 2B, but withonly a single wired backhaul connection 105 to the wired network. Inparticular, a single base site 120 is provided which is connected via awired backhaul connection 105 to the wired network 100. In addition, anumber of remote sites 130 are provided which incorporate the existingaccess base station functionality, but also incorporate a feederterminal associated therewith, allowing communication via the feeder airinterface to occur between the feeder base site 120 and the remote site130.

FIG. 4 illustrates how such an arrangement may be replicated to providea sectored wireless feeder network. In this example, two different typesof remote site are shown, the first being the tri-sector remote site 130where an access base station may use a known sectored antennae approachto communicate with items of end user equipment in the associated threesectors. Alternatively, the single feeder terminal at the remote sitemay serve multiple access base stations and so can eliminate redundantdownlink broadcast and multicast traffic. The second type of remote siteis an omni remote site 140 where an omni directional antenna is used tocommunicate with items of end user equipment within the associatedsector. It will be appreciated that, by virtue of the use of thewireless feeder network, a significant reduction in the wired backhaulrequirement is achieved. Further, due to the techniques employed inembodiments to ensure that the wireless feeder air interface is veryspectrally efficient, the wireless backhaul functionality provided bythe wireless feeder network has only a small impact on the overallamount of wireless resource available to carry traffic within the accessnetwork.

FIG. 5A schematically illustrates a plurality of layers of the wirelessfeeder network. The first layer 155 is the feeder network controllerlayer, and in this embodiment comprises a single feeder networkcontroller 150. The next layer is a feeder base station layer 160 and inthis example includes eight feeder base stations 161 to 168 which areall controlled via the feeder network controller 150.

The next layer 170 is a feeder terminal controllability layer andidentifies which feeder terminals are controlled by which feeder basestations. Accordingly, each of the feeder base stations 161 to 168 isarranged during use of the wireless feeder network to communicate withthose feeder terminals within its associated controllability region 171to 178, respectively. Whilst the controllability regions can be amendedif desired, in one embodiment it is assumed that the controllabilityregions are relatively static. In one embodiment, the controllabilityregions are assigned by the feeder network controller. As a new feederterminal is deployed, it will be allocated to one of the feeder basestations, and will hence be contained within that feeder base station'scontrollability region. Between each feeder terminal and its associatedfeeder base station, a feeder link will be established over which dataand control messages will pass between the feeder base station and afeeder terminal.

However, it will be apparent that in a typical deployment, a feederterminal may be in a position to listen to another one or more feederbase stations in addition to its allocated feeder base station. Theinformation as to which feeder base stations each feeder terminal isable to see communications from can be determined during a soundingprocess that will be described in more detail later. That soundingprocess produces a visibility matrix defining a plurality of visibilityregions as shown by the layer 180 in FIG. 5B. It will be appreciatedfrom a comparison of FIG. 5B with FIG. 5A that each visibility region181 to 188 is somewhat larger than the associated controllabilityregion, and by its nature the visibility regions will overlap. Forexample, considering FIG. 5B, it is noted that feeder terminal 9 mayconnect to or be interfered with by signals originating from feeder basestations 161, 162 or 163. Thus, a visibility region contains any feederterminal that a feeder base station can communicate to or interferewith.

In order initially to configure the wireless feeder network, and tomonitor its performance on an ongoing basis, the feeder networkcontroller 150 in FIGS. 5A and 5B is configured to control soundingprocedures in the wireless feeder network. During a sounding process anelement of the wireless feeder network (e.g. a selected feeder basestation) transmits a known sounding signal and the feeder terminalswhich are able to receive that signal then perform downlink soundingmeasurements. A similar procedure is carried out to perform uplinksounding measurements wherein a feeder terminal transmits a knownsounding signal to be received by the feeder base stations which havevisibility of that feeder terminal. Sounding yields various channelmetrics that include (but are not limited to): channel impulseresponses, complex channel frequency responses, frequency dependentco-variance matrices of the received signals, frequency dependenteigenmodes, and so on. Building up a set of channel metrics in thismanner for the whole wireless feeder network provides a system-wide viewof the quality of the wireless channels in the network.

In an established wireless feeder network, there is typically a welldefined relationship between feeder base stations and feeder terminals,wherein any given feeder terminal is uniquely associated with one feederbase station (see FIG. 5A). However, due to the overlapping nature ofthe visibility regions (see FIG. 5B), coordination is required whenperforming the above-described sounding processes, such that the sourceof a given sounding signal is precisely defined. For example, withreference to FIG. 5B, if feeder terminal 9 were to be configured toreceive a downlink sounding signal, without coordination between feederbase stations 161, 162 and 163, it would not be possible for feederterminal 9 to identify which feeder base station was the source of agiven sounding signal. Worse still, if feeder base stations 161, 162 and163 were to transmit sounding signals at the same time (or at least inoverlapping time windows), these signals would interfere and result inan incorrect downlink sounding measurement being performed by feederterminal 9. Similarly, uplink sounding measurements made by a givenfeeder base station can also suffer from interference between uplinksounding signals transmitted by more than one feeder terminal.

The basic steps involved in performing coordinated sounding in thewireless feeder network are schematically illustrated in FIG. 6. At step200 the process is started, whereafter at step 202 a global soundingprocess is carried out. Global sounding is a network-wide exhaustivesounding method utilising fully orthogonal (non-overlapping) soundingschedules used to generate a visibility matrix which indicates thevisibility between feeder base stations and feeder terminals. The feedernetwork controller 150 controls this process, such that each feeder basestation performs downlink sounding in turn, whereafter each feederterminal performs uplink sounding in turn. This process is described inmore detail with reference to FIGS. 8-12.

Once the global sounding process has been carried out, at step 204 thefeeder network controller computes the visibility matrix for the network(or updates a pre-existing visibility matrix, if one exists). On thebasis of the visibility matrix, the feeder network controller can thenconfigure the wireless feeder network, for example determining thecontrollability regions illustrated in FIG. 5A and allocating thewireless resource available to the feeder network. The flow in FIG. 6proceeds to step 206, where it is determined if a new feeder basestation or feeder terminal has been added to the network. If it has,then at step 208 a hypothesised visibility matrix is generated by thefeeder network controller including the new feeder base station orfeeder terminal. This can be done on the basis of the geographicallocation of the new feeder base station or feeder terminal and otherknowledge about the local transmission conditions to produce thehypothesised visibility matrix. In general the hypothesised visibilitymatrix will be set up as an overestimate of the visibility of the newnetwork element, so as to ensure that all possible interferences aredetermined. On this basis at step 210 an initial sounding process iscarried out to test the actual visibility of the new feeder base stationor feeder terminal with respect to the existing wireless network and onthe basis of that sounding process at step 212 the visibility matrix canbe re-calculated and updated. The flow then returns to step 206. Furtherdetail of the initial sounding process carried out when a new feederbase station or feeder terminal is added to the wireless network isdescribed hereinafter with reference to FIGS. 13-17.

Alternatively at step 206, if it is determined that no new feeder basestations or feeder terminals have been added to the wireless feedernetwork, then at step 214 periodic sounding may be carried out. Periodicsounding is a slow rate, highly parallelised sounding scheme which iscarried out as a background process whilst the wireless feeder networkis transmitting its usual network traffic. It is carried out so as toensure minimum interference between the sounding process itself and thenetwork traffic. Further details of the periodic sounding process aredescribed hereinafter with reference to FIGS. 18-22. After step 206, aswell as the periodic sounding at step 214, the feeder network controllermay also (step 216) control a global sounding epoch in the wirelessfeeder network. In order for this global sounding epoch to be carriedout whilst periodic sounding (step 214) is also happening, it isnecessary for a multiple access scheme such as time division multipleaccess (TDMA), frequency division multiple access (FDMA), code divisionmultiple access (CDMA) or combinations of these three to be used toseparate the respective sounding signals from one another. On the basisof a further global sounding epoch, at step 218 the visibility matrixcan be determined and updated. Thereafter the flow returns to step 206.

FIG. 7 schematically illustrates the configuration of the feeder networkcontroller. Feeder network controller 220 contains sounding schedulecomputation circuitry 222 for computing and updating sounding schedulesand visibility matrices. Via the input interface 224, the soundingschedule computation circuitry receives sounding data from the networkwhich provides the information from which the visibility matrix can bedetermined (item 226). The sounding data received at input 224, togetherwith the visibility matrix, provides the basis for determining theuplink and downlink schedules (item 228) within the sounding schedulecomputation circuitry 222. The sounding schedule computation circuitry222 also has reference to a database 230 wherein previously determinedvisibility matrices and uplink/downlink sounding schedules may be storedas well as other configurational parameters. Once determined, the uplinkand downlink schedules are distributed to the network via distributioninterface 232 to cause the determined schedules to be carried out.

FIG. 8 illustrates a first stage in the setting up of a wireless feedernetwork comprising three feeder base stations FBS₁₋₃ and 14 feederterminals (FT₁₋₁₄). The first step in, setting up this new wirelessfeeder network is to determine the visibility matrix representing thevisibility of the feeder base stations and feeder terminals for oneanother. To do this a global sounding procedure is coordinated by thefeeder network controller. The global sounding process comprises adownlink sounding process followed by an uplink sounding process.

The downlink sounding schedule is represented in FIG. 8 by the orderedlists D_(FBS) and D_(FT). The downlink sounding schedule has threeepochs which can be most easily seen from D_(FBS) which shows theordering in which the feeder base stations perform their downlinksounding, namely first FBS₁, then FBS₂, and finally FBS₃.Correspondingly, D_(FT) shows the configuration of the feeder terminalsfor receiving the downlink sounding signals transmitted by the feederbase stations in each epoch. It can be seen that all 14 feeder terminalsare configured to receive downlink sounding signals in each of the threeepochs.

Conversely, the uplink sounding schedule is shown by U_(FT) and U_(FBS).Here, there are 14 epochs corresponding to the 14 feeder terminals.U_(FT) shows that each feeder terminal takes its turn in one epoch totransmit its uplink sounding signals, whilst U_(FBS) shows that in eachof the 14 epochs all three feeder base stations are configured toreceive uplink sounding signals.

In other words, during the downlink sounding schedule each feeder basestation takes a turn to transmit downlink sounding signals whilst allfeeder terminals listen and during the uplink sounding schedule eachfeeder terminal takes a turn to transmit uplink sounding signals, whilstall three feeder base stations listen.

FIG. 9 is a flow diagram illustrating the steps performed by the feedernetwork controller to coordinate a global sounding process. At step 250,the process is started, whereafter at step 252 the feeder networkcontroller sets a variable N corresponding to the number of feeder basestations and a variable M corresponding to the number of feederterminals. At step 254 the exhaustive set of uplink and downlink globalsounding schedules is then determined, the number of epochs in thedownlink schedule D_(FBS) and D_(FT) being defined by the number offeeder base stations N and the number of epochs in the uplink soundingschedule U_(FT) and U_(FBS) being determined by the number of feederterminals M. Having generated the global sounding schedules, at step 256the downlink sounding is carried out (described in more detail withreference to FIG. 10) and at step 258 the uplink sounding is carried out(described in more detail with reference to FIG. 11). The globalsounding procedure completes at step 260.

The downlink sounding process is now described with reference to thesteps illustrated in the flow diagram shown in FIG. 10. The processbegins at step 270, whereafter at step 272 the counter n (used to trackthe epoch number) is set to 0. The process then enters the loopbeginning at step 274, where n is incremented by 1. At step 276 thefeeder base stations indicated in epoch n of downlink schedule D_(FBS)transmit their downlink sounding signal. It should be noted the FIG. 10represents a generic downlink sounding process according to which it ispossible for feeder base stations to perform downlink soundingsimultaneously. Hence in FIG. 10 step 276 is illustrated as a number ofsimultaneous downlink sounding steps (276A, 276B . . . 276C). However,when downlink sounding is being performed as part of a global soundingschedule (i.e. at step 256 in FIG. 9), only one feeder base station willtypically perform downlink sounding per epoch and hence only onesub-step (step 276A) will exist at step 276. In the more general case(discussed later on) when simultaneous downlink sounding may be allowed,several feeder base stations may transmit downlink sounding signals atthe same time. The number of sub-steps at step 276 is given (see step276C) by |D_(FBS)(n)| (i.e. the number of feeder base stations listed inthe n^(th) element of D_(FBS)).

The flow in FIG. 10 then proceeds to step 278 (illustrated as parallelsub-steps 278A-C), where the feeder terminals indicated in epoch n ofdownlink schedule D_(FT) receive the downlink sounding signal(s). Thenumber of feeder terminals arranged to receive downlink sounding signalsin epoch n determines how many parallel sub-steps are carried out atstep 278, the number being given by the size of |D_(FT)(n)| (i.e. thenumber of feeder terminals listed in the n^(th) element of D_(FT)).Following step 278, at step 280 (i.e. sub-steps 280A-C as appropriate)the downlink channel metrics measurable on the basis of the soundingsignals transmitted and received in this epoch are computed and storedin the feeder network controller.

Finally at step 282 it is determined if n (the epoch counter) is lessthan the total number of epochs in the downlink sounding schedule, givenby |D_(FBS)|. If it is, then the flow returns to step 274 for n to beincremented and the next epoch to be performed. Once all epochs of thedownlink sounding schedule have been performed, the flow concludes atstep 284.

The uplink sounding procedure is carried out in an analogous fashion tothe downlink sounding procedure and FIG. 11 is a flow diagramillustrating the basic steps carried out when performing uplinksounding. The process begins at step 290, whereafter at step 292 thecounter m (used to track the epoch number) is set to 0. The process thenenters the loop beginning at step 294, where m is incremented by 1. Atstep 296 the feeder terminals indicated in epoch m of uplink scheduleU_(FT) transmit their uplink sounding signal. As noted with reference toFIG. 10, it should also be noted with reference to FIG. 11 that thefigure also represents a generic uplink sounding process according towhich it is possible for feeder terminals to perform uplink soundingsimultaneously. Hence in FIG. 11 step 296 is illustrated as a number ofsimultaneous downlink sounding steps (296A, 296B . . . 296C). However,when uplink sounding is being performed as part of a global soundingschedule (i.e. at step 258 in FIG. 9), only one feeder terminal stationwill typically perform downlink sounding per epoch and hence only onesub-step (step 296A) will exist at step 296. In the more general case(discussed later on) when simultaneous uplink sounding may be allowed,several feeder terminals may transmit uplink sounding signals at thesame time. The number of sub-steps at step 296 is given (see step 296C)by |U_(FT)(m)| (i.e. the number of feeder terminal listed in the m^(th)element of U_(FT)).

The flow in FIG. 11 then proceeds to step 298 (illustrated as parallelsub-steps 298A-C), where the feeder base stations indicated in epoch mof uplink schedule U_(FBS) receive the uplink sounding signal(s). Thenumber of feeder base stations arranged to receive uplink soundingsignals in epoch m determines how many parallel sub-steps are carriedout at step 298, the number being given by the size of |U_(FBS)(m)|(i.e. the number of feeder base stations listed in the m^(th) element ofU_(FBS)). Following step 298, at step 300 (i.e. sub-steps 300A-C asappropriate) the uplink channel metrics measurable on the basis of thesounding signals transmitted and received in this epoch are computed andstored in the feeder network controller.

Finally at step 302 it is determined if m (the epoch counter) is lessthan the total number of epochs in the uplink sounding schedule, givenby |U_(FT)|. If it is, then the flow returns to step 274 for m to beincremented and the next epoch to be performed. Once all epochs of theuplink sounding schedule have been performed, the flow concludes at step304.

FIG. 12 illustrates the result of the global sounding proceduredetermined for the example network of FIG. 8 in terms of the determinedvisibility between the feeder base stations and the feeder terminals.Feeder base station FBS₁ has visibility of feeder terminals FT₁₋₃, FT₁₃and FT₁₄; feeder base station FBS₂ has visibility of feeder terminalsFT₁₁₋₁₃; and feeder base station FBS₃ has visibility of feeder terminalsFT₃₋₁₃. This is also represented by the visibility matrix V, wherein thecolumns correspond to feeder base stations and the rows correspond tofeeder terminals. Thus determined, the visibility matrix is stored bythe feeder network controller in its database 230 to form the basis offurther configuration of the wireless feeder network.

FIG. 13 schematically illustrates the feeder wireless network discussedwith reference to FIG. 12, wherein an additional feeder base station(FBS₄) has been added. When a new feeder base station is added to thewireless feeder network, it first identifies itself to the feedernetwork controller indicating that it wishes to join the network. Inresponse to this the feeder network controller determines a hypothesisedvisibility matrix which includes the new feeder base station. Thehypothesised visibility matrix is an adaptation of the visibility matrixgenerated previously during global sounding an illustrated in FIG. 12.As can be seen in the visibility matrix illustrated in FIG. 13, for anew feeder base station this involves the addition of a column to thepreviously generated visibility matrix. Furthermore, the new column ispopulated in accordance with the hypothesis for which feeder terminalsin the existing wireless feeder network the new feeder base station mayhave visibility. Based on the geographical location of the existingfeeder terminals and the geographical location of the new feeder basestation FBS₄, it is hypothesised that FBS₄ may have visibility of feederterminals FT₁₋₈. It should be noted that in general the hypothesisrepresents an over-estimate of the visibility, to ensure that allpossible interferences generated by the introduction of new feeder basestation FBS₄ are taken into account.

FIG. 13 also illustrates a sounding schedule generated in accordancewith the hypothesised visibility matrix shown. Like the global soundingschedule, this sounding schedule is an exhaustive procedure, but onlycovers those elements of the new wireless feeder network that involve(or are at least hypothesised to involve) the new feeder base stationFBS₄. Hence, for the downlink sounding schedule there is only one epoch,wherein FBS₄ transmits its downlink sounding signal and during which alleight of the feeder terminals which are hypothesised to have avisibility of FBS₄ are configured to receive the downlink soundingsignal. Conversely, in the uplink sounding schedule there are eightepochs, wherein each of the eight feeder terminals takes its turn totransmit its uplink sounding signal. Note that during the uplinksounding procedure, not only does the new feeder bases station FBS₄listen at each epoch, but also those feeder base stations which arealready known to have visibility of the corresponding feeder terminalfrom the previous global sounding procedure. Hence, for example, in thefirst epoch of the uplink sounding schedule, both FBS₁ and FBS₄ listenwhen feeder terminal 1 is transmitting its uplink sounding schedule.

FIG. 14 is a flow diagram illustrating the basic steps carried out toperform an initial sounding process, such as that carried out when a newelement has been added to the wireless feeder network (such as theaddition of a new feeder base station discussed with reference to FIG.13). The flow begins at step 320, whereafter at step 322, the totalnumber of feeder base stations N and the total number of feederterminals M is obtained by the feeder network controller 220. The feedernetwork controller 220 also retrieves the hypothesised visibility matrixgenerated in response to the signing on of the new feeder base stationor feeder terminal to the wireless network. At step 324 it is determinedwhether the new element is a feeder base station or not. If it is thenthe flow proceeds to step 326, where the index n of the new feeder basestation is obtained. Then, at step 328, downlink and uplink soundingschedules for initial sounding in response to the addition of the newfeeder base station are generated. For a single new feeder base stationthere is only one downlink sounding epoch, whilst there will be as manyuplink sounding epochs as there are feeder terminals which havevisibility of the new feeder base station, i.e. allowing the new feederbase station to listen to each of those feeder terminals in turn. Thisnumber of feeder terminals is given by |D_(FT)[1]| (i.e. the number ofreceiving feeder terminals listed for the one downlink sounding epoch).

For each of these |D_(FT)[1]| uplink sounding epochs, the feeder basestations configured to receive the uplink sounding signals are thoseindicated by the hypothesised visibility matrix to have visibility ofthe feeder terminal performing uplink sounding in that epoch. Hence ineach of the |D_(FT)[1]| uplink sounding epochs (alternatively written as|U_(FT)| uplink sounding epochs) the feeder base stations are thosehaving visibility of feeder terminals listed in U_(FT)(1)(l), where lruns from one to |U_(FT)|. Once the initial downlink and uplink soundingschedules have been generated in this manner they are carried out atsteps 334 and 336 respectively.

Conversely if at step 324 it is determined that it is not a new feederbase station that has been added to the network, this means that it is afeeder terminal that has been added and at step 330 the index m of thenew feeder terminal is obtained. Then at step 332 uplink and downlinksounding schedules for the initial sounding process are derived.

With the addition of a new feeder terminal there will be only one uplinksounding epoch, during which the new feeder terminal transmits itsuplink sounding signal and all feeder base stations which are indicatedby the hypothesised visibility matrix to have visibility of that feederterminal are configured to receive the uplink sounding signal.Conversely, for the downlink sounding schedule there will be as manyepochs as there are feeder base stations which are hypothesised ashaving visibility of the new feeder terminal, this number being given byU_(FBS)[1]. In each of these epochs all feeder terminals which areindicated by the hypothesised visibility matrix to have visibility ofthe feeder base station which is sounding in that epoch will beconfigured to receive the downlink sounding signal, i.e. the feederterminals are those having visibility of the feeder base stations listedin D_(FBS)(1)(l), where l runs from one to |D_(FBS)|. When the initialdownlink and uplink sounding schedules corresponding to the introductionof the new feeder terminal have been generated in this manner thedownlink sounding is performed at step 334 and the uplink sounding isperformed at step 336. The initial sounding process is complete at step338.

FIG. 15 illustrates the wireless feeder network in terms of visibilityregions once the visibility matrix has been updated after the initialsounding process described with reference to FIG. 14 has been carriedout. As can be seen from the illustrated visibility regions and from thevisibility matrix, the initial sounding procedure has revealed that infact feeder base station FBS₄ only has visibility of feeder terminalsFT₆ and FT₇. Hence the hypothesised visibility for new feeder basestation FBS₄ has been reduced from indicating feeder terminals FT₁₋₈down to only feeder terminals FT₆ and FT₇.

On the basis of the updated visibility matrix, which the feeder networkcontroller 320 stores in database 230, the feeder network controller canthen configure the updated wireless feeder network both in terms of howregular network traffic will be transmitted, for example where feederterminals FT₆ and FT₇ previously had to be controlled by feeder basestation FBS₃, either feeder terminal could now be associated with newfeeder base station FBS₄, freeing up capacity for feeder base stationFBS₃.

FIG. 16 schematically illustrates the addition of a further element tothe wireless feeder network, namely an additional feeder terminal FT₁₅.From the geographical location of the new feeder terminal FT₁₅, it ishypothesised that this new feeder terminal in the wireless feedernetwork may be visible to original feeder base stations FBS₁ and FBS₃and also to the recently added feeder base station FBS₄. This is alsorepresented by a revised hypothesised visibility matrix having anadditional row illustrating this hypothesis. The initial soundingprocedure corresponding to the addition of this new feeder terminal isalso illustrated in FIG. 16. The single new feeder terminal FT₁₅ resultsin a single uplink sounding epoch in which feeder terminal FT₁₅transmits its uplink sounding signal and (based on the hypothesisedvisibility matrix) feeder base stations FBS₁, FBS₃ and FBS₄ listen forthe uplink sounding signal. Conversely during downlink sounding thereare three epochs corresponding to the three feeder base stationshypothesised to have visibility of feeder terminal FT₁₅. During each ofthe downlink sounding epochs the feeder terminals indicated by thehypothesised visibility matrix have visibility of the correspondingfeeder base station are configured to listen for the downlink soundingsignal.

After the initial sounding process corresponding to the addition of newfeeder terminal FT₁₅ has been carried out (according to the processdescribed with reference to FIG. 14), the results are shown in FIG. 17.

FIG. 17 schematically illustrates the visibility within the wirelessfeeder network after the initial sounding process has been carried outfollowing the addition of feeder terminal FT₁₅. As can be seen from theillustrated visibility regions and the updated visibility matrix, theinitial sounding process has revealed that in fact feeder terminal FT₁₅is only visible to feeder base station FBS₃ and not to feeder basestations FBS₁ and FBS₄ as hypothesised. This updated visibility matrixcan then be stored by feeder network controller 220 in database 230 tobe referred to when further configuring the wireless feeder network.

As well as the global sounding procedure and initial sounding procedurecarried out when setting up a wireless feeder network (or a newcomponent thereof), a further sounding process may be carried out oncethe wireless feeder network is established to monitor its performanceand keep track of any changes in the channel metrics for the wirelesschannels in the network. This process is known as periodic sounding andis a slow rate, highly parallelised sounding procedure. Periodicsounding is coordinated by the feeder network controller such thatminimum interference takes place. That is to say, the visibility matrixgives the feeder network controller the information necessary to performperiodic sounding such that the sounding may be carried out in parallelby components of the wireless feeder network which are known to have nointerference overlap. This enables the periodic sounding procedure to becarried out more efficiently, since wireless channels in the networkwhich are known to have no interference with one another can besimultaneously sounded.

The general procedure for carrying out periodic sounding isschematically illustrated in FIG. 18. The flow begins at step 400,whereafter at step 402 the feeder network controller obtains the numberof feeder base station (N), the number of feeder terminals (M) and thepreviously determined visibility matrix (V). Thereafter at step 404 thefeeder network controller determines D_(FBS), namely the downlinksounding (transmission) list for the feeder base stations (described inmore detail hereinafter with reference to FIG. 19). At step 406 thefeeder network controller determines D_(FT), namely the downlinksounding (reception) list for the feeder terminals (described in moredetail hereinafter with reference to FIG. 20). At step 408, the downlinksounding process is then carried out (according to the procedurepreviously described with reference to FIG. 10). At step 410 the feedernetwork controller determines U_(FT), namely the uplink sounding(transmission) list for the feeder terminals (described in more detailhereinafter with reference to FIG. 21) and at step 412 the feedernetwork controller calculates U_(FBS), namely the uplink sounding(reception) list for the feeder base station (described in more detailhereinafter with reference to FIG. 22). At step 414, the uplink soundingprocedure is then carried out (as previously described with reference toFIG. 11). The procedure is then complete at step 416. It will beappreciated that the sequence of steps illustrated in FIG. 18 is onlyone example, and it would of course be possible for both downlinksounding and uplink sounding to be carried out after the necessarysounding lists have been calculated (i.e. step 408 could follow step412). Alternatively, uplink sounding could precede downlink sounding andso on.

The calculation of D_(FBS) is now described in more detail withreference to FIG. 19. The flow begins at step 440, and at step 442 thefeeder network controller calculates the matrix product V^(T)V (i.e. thetranspose of the visibility matrix multiplied by the visibility matrix)to give square matrix D, which is an N by N square matrix showing theinterference between feeder base stations. Off-diagonal elements of thismatrix indicate where interference between feeder base stations isexpected to occur. Also at step 442 the feeder network controllerprepares a one-dimensional vector a populated by N ones, i.e. a is avector of length N, corresponding to the number of feeder base stations.Then at step 444 the variable j representing the epoch number and thevariable m representing the feeder base station number are each set to0.

The flow then enters a loop, beginning at step 446, in which each feederbase station will be considered in turn. At step 446 m is incremented by1, i.e. during the first iteration of this loop m is set to 1. Then atstep 448 it is determined whether m is greater than N, i.e. if allfeeder base stations have been considered in this loop. If they havenot, then the flow proceeds to step 450, where it is checked if a(m) isgreater than 0, i.e. if the m^(th) element of vector a has been changedfrom its initial value of zero. The vector a is used to track whichfeeder base stations have already been included in the downlink soundingschedule, where a one indicates it has not yet been used. Hence when (atstep 450) it is determined that the currently considered feeder basestation has not yet been used in the downlink schedule, the flowproceeds to step 452 where a(m) is set to 0 (indicating that this feederbase station has now been used). Also at step 452, the epoch number isincremented by 1 and m (the FBS currently under consideration) is set asthe first entry in this j^(th) epoch of the downlink sounding schedule.Then at step 454 the variable n is set to the current value of m, andthe flow proceeds to step 456.

Steps 456 and 458 initiate a sub-loop in which the remaining feeder basestations (i.e. FBS_(m+1) to FBS_(N)) are considered in order todetermine if any of these feeder base stations can perform theirdownlink sounding simultaneously with the feeder base station FBS_(m)under consideration in the main loop (steps 446-450). At step 456 n isincremented by 1 and at step 458 the variable k is set to 0. The loopthen begins at step 460 where k is incremented by 1. Variable k is usedas the index for the number of feeder base stations occurring in a givenepoch. Then at step 462 it is determined if a(n) equals 0 (indicatingthat feeder base station FBS_(n) has already been used and allocated toa sounding epoch) or if D(D_(FBS)(j)(k), n) is greater than 0 (i.e. ifthe FBS interference matrix D has an entry indicating that FBS_(n) willinterfere with another feeder base station (referenced by index k)already listed at this epoch (referenced by index j) of the downlinksounding schedule D_(FBS)).

If neither of these conditions at step 462 is true then flow proceeds tostep 464, where it is determined if k is less than |D_(FBS)(j)| (i.e. iffor this epoch all existing entries in the downlink sounding schedulehave been considered). If k is less than this value then flow returns tostep 460 to increment k and loop over all entries in the current epoch.Otherwise the flow proceeds to step 466. Step 466 is reached if it isestablished that FBS_(n) does not interfere with the main loop feederbase station FBS_(m), or any of the other feeder base stations in theepoch currently under consideration. Thus at step 466 n is appended tothe listed feeder base stations for the current epoch and a(n) is set to0, indicating that this feeder base station has been used in thedownlink sounding schedule. The flow then proceeds to step 468 (whichstep is also reached from step 462 if either of the conditions testedthere are true), where it is tested if n is less than N, i.e. if allfurther feeder base stations (m+1 up to N) have been considered. If theyhave not the flow returns to step 456. If they have, the flow proceedsto step 470 where it is tested if m is less than N (i.e. if all feederbase stations in the main loop have been considered). If they have notthen the flow returns to step 446, m is incremented by 1 and the nextfeeder base station is considered. Once all feeder base stations havebeen considered the flow concludes at step 472. Hence, according to theflow described in FIG. 19, the feeder network controller can determine adownlink sounding schedule for the feeder base stations, systematicallydetermining which feeder base stations may be allocated to the sameepoch and therefore perform their downlink sounding simultaneously.

The calculation of D_(FT) by the feeder network controller is nowdescribed in more detail with reference to the flow diagram illustratedin FIG. 20. The flow begins at step 480, whereafter at step 482 theepoch index m is set to 0. At step 484 the epoch m is incremented by 1and at step 486 the variable n is set to 0. The variable n is used toloop over all feeder base stations indicated in a given epoch of theschedule D_(FBS). Then at step 488 n is incremented by 1 and thevariable j is set to 0. The variable j is used as an index over thenumber of feeder terminals which are required to receive the downlinksignal in any given epoch. Then at step 490 the variable k is set to 0,where k is a variable used to loop over all feeder terminals.

The flow proceeds to step 492, where k is incremented by 1. Then at step494 it is determined if the visibility matrix indicates visibilitybetween the current feeder terminal under consideration (k) and then^(th) feeder base station indicated by the downlink sounding scheduleD_(FBS) for the current epoch. If there is visibility between thisfeeder terminal/feeder base station pair, then the flow proceeds viastep 496 where the variable j is incremented by 1 and the downlinksounding schedule for the feeder terminals D_(FT) adds feeder terminal kas an additional entry in epoch m. The flow proceeds to step 498 whereit is determined if all feeder terminals have been considered (i.e. if kis less than M). If there are still feeder terminals to consider theflow returns to step 492. Once all feeder terminals have been consideredthe flow proceeds to step 500, at which it is determined if all feederbase stations listed in D_(FBS) for the current epoch have beenconsidered (i.e. if variable n is less than |D_(FBS)(m)|). If there arefurther feeder base stations in the current epoch to consider the flowreturns to step 488, where n is incremented by 1. Once all feeder basestations in the current epoch have been considered, the flow proceeds tostep 502 where it is determined if all epochs have been considered (i.e.if variable m is less than |D_(FBS)|). If there is a further epoch toconsider then flow returns to step 484, and once all epochs have beenconsidered the flow concludes at step 504.

The calculation of U_(FT) is now described in more detail with referenceto FIG. 21. The flow begins at step 510, and at step 512 the feedernetwork controller calculates the matrix product VV^(T) (i.e. thevisibility matrix multiplied by the transpose of the visibility matrix)to give square matrix U, which is an M by M square matrix showing theinterference between feeder terminals. Off-diagonal elements of thismatrix indicate where interference between feeder terminals is expectedto occur. Also at step 512 the feeder network controller prepares aone-dimensional vector a populated by M ones, i.e. a is a vector oflength M, corresponding to the number of feeder terminals. Then at step514 the variable j representing the epoch number and the variable mrepresenting the feeder terminal number are each set to 0.

The flow then enters a loop, beginning at step 516, in which each feederterminal will be considered in turn. At step 516 m is incremented by 1,i.e. during the first iteration of this loop m is set to 1. Then at step518 it is determined whether m is greater than M, i.e. if all feederterminals have been considered in this loop. If they have not, then theflow proceeds to step 520, where it is checked if a(m) is greater than0, i.e. if the element of vector a has been changed from its initialvalue of zero. The vector a is used to track which feeder terminals havealready been included in the uplink sounding schedule, where a oneindicates it has not yet been used: Hence when (at step 520) it isdetermined that the currently considered feeder terminal has not yetbeen used in the uplink schedule, the flow proceeds to step 522 wherea(m) is set to 0 (indicating that this feeder terminal has now beenused). Also at step 522, the epoch number is incremented by 1 and m (theFT currently under consideration) is set as the first entry in thisj^(th) epoch of the uplink sounding schedule. Then at step 524 thevariable n is set to the current value of m, and the flow proceeds tostep 526.

Steps 526 and 528 initiate a sub-loop in which the remaining feeder basestations (i.e. FT_(m+1) to FT_(M)) are considered in order to determineif any of these feeder terminals can perform their uplink soundingsimultaneously with the feeder terminal FT_(m) under consideration inthe main loop (steps 516-520). At step 526 n is incremented by 1 and atstep 528 the variable k is set to 0. The loop then begins at step 530where k is incremented by 1. Variable k is used as the index for thenumber of feeder terminals occurring in a given epoch. Then at step 532it is determined if a(n) equals 0 (indicating that feeder terminalFT_(n) has already been used and allocated to a sounding epoch) or ifU(U_(FT)(j)(k), n) is greater than 0 (i.e. if the FT interference matrixU has an entry indicating that FT_(n) will interfere with another feederterminal (referenced by index k) already listed at this epoch(referenced by index j) of the uplink sounding schedule U_(FT)).

If neither of these conditions at step 532 is true then flow proceeds tostep 534, where it is determined if k is less than |U_(FT)(j)| (i.e. iffor this epoch all existing entries in the uplink sounding schedule havebeen considered). If k is less than this value then flow returns to step530 to increment k and loop over all entries in the current epoch.Otherwise the flow proceeds to step 536. Step 536 is reached if it isestablished that FT_(n) does not interfere with the main loop feederterminal FT_(m), or any of the other feeder terminals in the epochcurrently under consideration. Thus at step 536 n is appended to thelisted feeder terminals for the current epoch and a(n) is set to 0,indicating that this feeder terminal has been used in the uplinksounding schedule. The flow then proceeds to step 538 (which step isalso reached from step 532 if either of the conditions tested there aretrue), where it is tested if n is less than M, i.e. if all furtherfeeder terminals (m+1 up to M) have been considered. If they have notthe flow returns to step 526. If they have, the flow proceeds to step540 where it is tested if m is less than M (i.e. if all feeder terminalsin the main loop have been considered). If they have not then the flowreturns to step 516, m is incremented by 1 and the next feeder terminalis considered. Once all feeder terminals have been considered the flowconcludes at step 542. Hence, according to the flow described in FIG.21, the feeder network controller can determine an uplink soundingschedule for the feeder terminals, systematically determining whichfeeder terminals may be allocated to the same epoch and thereforeperform their uplink sounding simultaneously.

The calculation of U_(FBS) by the feeder network controller is nowdescribed in more detail with reference to the flow diagram illustratedin FIG. 22. The flow begins at step 560, whereafter at step 562 theepoch index m is set to 0. At step 564 the epoch m is incremented by 1and at step 566 the variable n is set to 0. The variable n is used toloop over all feeder terminals indicated in a given epoch of theschedule U_(FT). Then at step 568 n is incremented by 1 and the variablej is set to 0. The variable j is used as an index over the number offeeder base stations which are required to receive the uplink signal inany given epoch. Then at step 570 the variable k is set to 0, where k isa variable used to loop over all feeder base stations.

The flow proceeds to step 572, where k is incremented by 1. Then at step574 it is determined if the visibility matrix indicates visibilitybetween the current feeder base station under consideration (k) and then^(th) feeder terminal indicated by the uplink sounding schedule U_(FT)for the current epoch. If there is visibility between this feederterminal/feeder base station pair, then the flow proceeds via step 576where the variable j is incremented by 1 and the uplink soundingschedule for the feeder base stations U_(FBS) adds feeder base station kas an additional entry in epoch m. The flow proceeds to step 578 whereit is determined if all feeder base stations have been considered (i.e.if k is less than N). If there are still feeder base stations toconsider the flow returns to step 572. Once all feeder base stationshave been considered the flow proceeds to step 580, at which it isdetermined if all feeder terminals listed in U_(FT) for the currentepoch have been considered (i.e. if variable n is less than|U_(FT)(m)|). If there are further feeder terminals in the current epochto consider the flow returns to step 568, where n is incremented by 1.Once all feeder terminals in the current epoch have been considered, theflow proceeds to step 582 where it is determined if all epochs have beenconsidered (i.e. if variable m is less than |U_(FT)|). If there is afurther epoch to consider then flow returns to step 564, and once allepochs have been considered the flow concludes at step 584.

It should be noted that in the above discussion with reference to FIGS.8 to 22 the emphasis has been mainly on eliminating interference duringa sounding process by relying on spatial orthogonality. However itshould be appreciated that other multiple access schemes such asfrequency division (FDMA), time division (TDMA) or code division (CDMA)could also be used as alternatives or in addition to reduce the numberof sounding epochs required to be carried out.

As discussed earlier, to ensure that the wireless feeder networkprovides an efficient wireless backhaul, it is necessary for thewireless resource available to the wireless feeder network to be used inas spectrally efficient a manner as possible. The wireless resourcecomprises a plurality of resource blocks which can be considered to formorthogonal resources. Whilst these orthogonal resources can beestablished in a variety of ways, in one embodiment the wirelessresource is represented in two dimensions as shown in FIG. 23, namelythe time dimension (on the horizontal axis) and the frequency dimension(on the vertical axis). The wireless resource is sub-divided intohorizontal and vertical strips. The horizontal strips are calledsub-channels and the vertical strips are referred to as slots. In TimeDivision Multiple Access (TDMA), the entire frequency band is assignedto a single user. Multiple users share the radio spectrum bytransmitting at different time slots. In Frequency Division MultipleAccess (FDMA), each user is assigned to a fixed sub-channel.

In order to increase the system throughput, orthogonal resources may bereused throughout the network at a cost of increased intercellinterference. Interference may be reduced by employing well establishedreuse plans. Such schemes are generally not adaptive, are overlyconservative and thus do not permit the maximum utilisation of awireless feeder network.

In the proposed scheme, traffic-aware multiple access assignments(referred to herein as global schedules) are proposed. A global scheduleis a set of instructions on resource utilisation and the associatedanticipated network interference. Thus, a global schedule is anallocation of one or more subchannel/slot grids (referred to herein asresource blocks) to a number of feeder base stations (FBSs) to enabledownlink (DL) communication to a number of feeder terminals (FTs).Likewise, one or more resource blocks are allocated to a number of FTsto enable uplink (UL) communication. Furthermore, each resource blockincludes an instruction to support MIMO transmission and the associatednetwork wide co-channel interference. The feeder network controller(FNC) is responsible for computing and communicating the globalschedules to the FBSs. With the earlier described FIGS. 5A and 5B inmind, a straightforward resource block assignment that yields nointerference in the network is shown in FIG. 23. The square bracketednumbers denote the resource block id number. For the DL, (x,y) denotesthe transmission from FBS with index x to FT with index y, and for theUL, (x,y) denotes the transmission from FT with index x to FBS withindex y.

Since system wide channel metrics (derived from the sounding process)are available, the FNC can derive a global schedule with no intercellinterference that yields a significant increase in throughput. Anexample resource block assignment is shown in FIG. 24. Again, theresources are equally split among all users, but in contrast to FIG. 23,here the resources are reused without adding any intercell interference.

A further increase in throughput can take place by carefully examiningthe channel metrics and selecting sets of co-channel users with minimumco-channel interference. In the proposed scheme described herein, asystematic method is provided for computing global schedules bycarefully examining the channel metrics and taking traffic into account.Initially a global schedule is derived assuming uniform traffic loadingacross the network. However, FBSs monitor and report traffic loading tothe FNC, which in turn adapts the global schedule to meet the trafficdemands. The proposed algorithms are suitable for parallelisation.

A general outline of the process performed in accordance with oneembodiment in order to compute an initial global schedule and then toadapt that schedule based on reported traffic loading, will be describedfurther with reference to the flow diagram of FIG. 25. At step 650, thevarious feeder base stations and feeder terminals forming the wirelessfeeder network are deployed. Thereafter, a sounding process is performedat step 655, using the techniques described earlier. Based on thesounding information during the sounding process, a visibility matrix isgenerated at step 660. In particular this matrix will identify thevarious visibility regions for each of the feeder base stations.

Thereafter, at step 665, an initial global schedule is computed based onthe information in the matrix generated at step 660. This initial globalschedule can be computed in a variety of ways, but purely by way ofillustration, an example initial global schedule could be the onediscussed earlier with reference to FIG. 24 assuming the visibilityregions are as shown in the earlier described FIG. 5B. The globalschedule is then distributed to the feeder base stations and feederterminals at step 670, whereafter at step 675 the system goes live, i.e.is allowed to carry actual traffic.

During use, traffic reports will be sent to the feeder networkcontroller periodically from the various feeder base stations (step680). Based on this input, an evolutionary algorithm is applied tomodify the global schedule at step 685, whereafter a modified globalschedule is distributed at step 690.

It is expected that the time taken to perform the initial soundingprocess and to compute and distribute an initial global schedule will berelatively lengthy, for example of the order of 1 or 2 hours. However,if the schedule is then to be adapted to changing traffic conditions, itis clearly the case that modified global schedules must be capable ofbeing produced much more quickly. Due to the nature of the evolutionaryalgorithm used and the way in which it is applied to modify the globalschedule, it is possible to generate modified global schedules veryquickly, thereby enabling the global schedules to be changed in realtime to take account of changing traffic conditions. For example, in oneembodiment, the loop represented by steps 680, 685 and 690 may berepeated approximately every second.

The optimisation of the global schedules is performed using anEvolutionary Algorithm (EA), as for example described in T. Bäck,“Evolutionary Algorithms in Theory and Practice: Evolution Strategies,Evolutionary Programming, Genetic Algorithms”, Oxford University, 1996,T. Bäck, U. Hammel, and H. P. Schwefel, “Evolutionary computation:comments on the history and current state”, IEEE Transactions onEvolutionary Computation, vol. 1, pp. 3-17, April 1997(http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.6.5943[accessed 24-05-2010]), and Weise T., “Global Optimization Algorithms,Theory and Application”, http://www.it-weise.de/projects/book.pdf.

EAs are generic, population based, metaheuristic optimisationalgorithms, largely inspired by biological mechanisms, such as mutation,crossover (reproduction) and selection (see page 95 of theabove-mentioned “Global Optimization Algorithms, Theory and Application”document). The basic cycle of EAs is illustrated in FIG. 26, and itcomprises of five blocks (as discussed on page 96 of the above-mentioned“Global Optimization Algorithms, Theory and Application” document):

-   -   Initial Population (step 700)    -   Evaluation (step 705)    -   Fitness Assignment (step 710)    -   Selection (step 715)    -   Reproduction (step 720)

The reader is referred to the document “Global Optimization Algorithms,Theory and Application” for a general discussion on the functionalitiesof the above mentioned blocks (in addition to those pages mentionedabove, the reader may refer to pages 304 and 305). The followingdiscussion will describe how the basic evolutionary algorithm approachillustrated in FIG. 26 is adapted to enable its use in the currentsituation to provide rapid updates of global schedules based on changesin traffic conditions. However, in general terms, the initial populationstage 700 involves creating a set of individual entries, each individualentry in this case being an hypothesised global schedule. During theevaluation stage 705, each of the individuals in the population areevaluated, and hence in the current context the channel capacity forevery feeder link in the network is computed for each hypothesisedglobal schedule. Then, during fitness assignment step 710, for each linkthe channel capacity is converted to throughput by considering thenumber of resource blocks for each frame. This throughput is comparedagainst the target throughput and an associated reward is allocated toeach link. A reward can then be calculated for each hypothesised globalschedule.

The selection stage then involves applying a process to select theindividuals (i.e. the hypothesised global schedules) with high rewardsmore often than those with low rewards so that the individual entrieswith low fitness values will eventually be discarded and those with highvalues will enter the mating pool then used for the reproduction stage720. At the reproduction stage, pairs in the mating pool are selectedand for each pair offspring are created by combining or modifying theattributes of their parents. This results in a revised set ofhypothesised global schedules which can then be subjected to anotheriteration of the evolutionary algorithm.

Before describing in detail the manner in which the evolutionaryalgorithm of embodiments is used, the operation of the feeder networkcontroller will be described with reference to FIG. 27. The feedernetwork controller 750 contains global schedule computation circuitry755 for applying an evolutionary algorithm 760. Via the input interface765, the global schedule computation circuitry receives sounding datawhich provides, amongst other things, the visibility matrix identifyingthe visibility regions for each of the feeder base stations. Inaddition, via the input interface 770, the global schedule computationcircuitry 755 receives traffic reports from at least the feeder basestations deployed within the feeder network. Based on the sounding dataand traffic reports, the evolutionary algorithm is applied in order togenerate revised sets of hypotheses, each hypothesis representing aglobal schedule. As and when required, one of the current hypotheses ischosen to provide an updated global schedule, and that updated globalschedule is output to the various feeder base stations via thedistribution interface 775.

During application of the evolutionary algorithm 760, the globalschedule computation circuitry 755 will have reference to the database780 providing a number of network parameters required by theevolutionary algorithm. These network parameters will be discussed inmore detail later with reference to the relevant flow diagrams. An FNCto FNC interface 785 is provided for use in embodiments where multipleFNCs are used to manage the wireless feeder network, as will bediscussed in more detail later with reference to FIGS. 36A to 38.

FIG. 28 is a flow diagram illustrating the steps performed to computeand apply global schedules when a single feeder network controller isemployed in the network. At step 800, the process is started, whereafterat step 805 a variable N is set equal to the number of hypothesisedglobal schedules that are to be considered by the evolutionaryalgorithm. Thereafter, at step 810, a set of hypotheses are initialised.This process will be described in more detail later with reference toFIG. 29. Thereafter, a process of evaluating the various links betweenfeeder terminals and feeder base stations is performed at step 815, thisprocess being described later with reference to FIG. 30. Then, at step820, the current set of hypotheses are evaluated based on the output ofthe link evaluation process, in order to associate a reward with eachhypothesis in the set. This process will be described in more detaillater with reference to FIG. 32. Thereafter, a selection process isperformed at step 825 to select a modified set of hypotheses, thisprocess being described in more detail later with reference to FIG. 33.

Then, at step 830, a process is performed to determine and apply apreferred global schedule based on the modified set of hypothesesdetermined at step 825. For a system including a single feeder networkcontroller, this process will be described in more detail later withreference to FIG. 35. It should be noted that whilst in FIG. 28 step 830is shown as being performed on each iteration of the evolutionaryalgorithm, it does not need to be performed on each iteration, andinstead can be performed merely as and when a predetermined triggercondition occurs. This trigger condition may be completion of thecurrent iteration of the evolutionary algorithm, or may instead be aless frequently occurring trigger condition, such as an update to acertain traffic report, the receipt of updated sounding data, etc.

At step 835, a reproduction process is performed in order to produce areplacement set of hypotheses, after which the process returns to step815. The process at step 835 will be discussed in more detail later withreference to FIG. 34.

A more detailed discussion of the steps 810 to 835 of FIG. 28 will nowbe provided with reference to further flow diagrams.

Initialise Hypotheses

In this stage, multiple global schedule hypotheses are generated. Eachhypothesis corresponds to a candidate global schedule. In oneembodiment, an entry in the hypothesis consists of an UL or DLtransmission and:

-   -   1. Resource Block (RB) assignment, indicated by a FBS id, FT id        and a resource block (RB) id.    -   2. Multiple Input Multiple Output (MIMO) mode, specifying the        multi-antenna transmission scheme.    -   3. Transmit Precoding Matrix (TX PCM), instructing the        operations to map data streams onto antenna ports.    -   4. Receive Antenna Selection (RX AS), indicating one or more RX        antennas to be used.    -   5. Link Quality Indicator(s). One or more (depending on the MIMO        mode) data stream quality measures.    -   6. R_(r,n); covariance matrix of the interference as seen by the        receiver n on RB index r.

An example hypothesis is given in Table 1 below. For clarity, considerthe third row in Table 1. In this example, FBS₇ is linked to FT₄₀ in theDL transmitting on RB index 1. In addition, MIMO index 2, TX precodingmatrix index 2, LQI of 10 and the DL covariance matrix of theinterference are all specified.

TABLE 1 Example hypothesised global schedule. FBS FT UL/DL RB MIMO TXPCM RX AS LQI R 1  1 DL 1 2 2 0 8 RDL_(1,1) 4 19 DL 1 2 2 0 7 RDL_(1,19)7 40 DL 1 2 2 0 10  RDL_(1,40) . . . . . . . . . . . . . . . . . . . . .. . . . . . 5 29 DL 9 2 2 0 9 RDL_(9,29) 8 45 DL 9 2 2 0 7 RDL_(9,45) 1 1 UL 1 2 2 0 8 RUL_(1,1) 4 19 UL 1 2 2 0 10  RUL_(1,4) 40 UL 1 2 2 0 7RUL_(1,7) . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 20 UL9 2 2 0 8 RUL_(9,4) 6 31 UL 9 2 2 0 9 RUL_(9,6)

An example of MIMO modes applicable to a 2-transmit and 2-receiveantenna configuration is given in Table 2. Table 3 presents an exampleof Precoding Matrix modes for 2 TX antenna systems; antenna selection,beam steering and spatial multiplexing/transmit diversity are shown. Thetable could be extended to include improved granular beam angle steeringand beam shaping by applying different power ratios on the two transmitantennas. Antenna selection modes are given in Table 4. In this 2×2 MIMOcase the DL (FT/RB specific) interference matrices and the UL (FBS/RBspecific) interference matrices are also 2×2. Finally, the LQI is ameasure of the quality of the anticipated link. 10 may indicate the bestpossible link quality, where the highest modulation and code rate may beused.

TABLE 2 MIMO modes. MIMO id Description 0 Antenna Selection/Beamforming1 Cyclic Delay Diversity 2 Orthogonal Space Frequency Block Coding 3Orthogonal Space Time Block Coding 4 Spatial Multiplexing (horizontalencoding) 5 Spatial Multiplexing (vertical encoding)

TABLE 3 TX Precoding Matrix modes for 2 antennas. PCM id WeightsDescription 0 $\begin{bmatrix}1 \\0\end{bmatrix}\quad$ Select Antenna 1 1 $\begin{bmatrix}0 \\1\end{bmatrix}\quad$ Select Antenna 2 2$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}$ Rotate the phase on antenna 2 by 0 degrees 3$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}$ Rotate the phase on antenna 2 by 90 degrees 4$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}$ Rotate the phase on antenna 2 by 180 degrees 5$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}$ Rotate the phase on antenna 2 by 270 degrees 6$\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}$ Dual stream with uniform power allocation across TXantennas

TABLE 4 RX Antenna Selection modes for 2 antennas. PCM id WeightsDescription 0 $\begin{bmatrix}1 \\1\end{bmatrix}\quad$ Select all antennas 1 $\begin{bmatrix}1 \\0\end{bmatrix}\quad$ Select antenna 1 2 $\begin{bmatrix}0 \\1\end{bmatrix}\quad$ Select antenna 2

FIG. 29, illustrates the steps for generating multiple global schedulehypotheses. Following start of the process at step 850, from a databaseof Network Parameters 860 the number of FTs (L) and the controllabilitymatrix (C) are obtained at step 855. The controllability matrixindicates the set of valid FBS/FT feeder links in the network. In FIG.29, two iterations take place—the outer loop 867 generates N hypotheses,whereas the inner loop 869 will, for each hypothesis H_(n), assign oneor more resource blocks to each link, and assign a MIMO mode and a TXprecoding matrix to each resource block. Notice that the computation ofthe interference covariance matrices and the derivation of the LQIs havebeen omitted here. Their entries in the hypotheses are left empty, to becomputed during the evaluation phase of the algorithm.

Accordingly, considering FIG. 29 in more detail, a variable n is setequal to 0 at step 865, and it then incremented at step 870. Thereafter,a variable I is set equal to 0 at step 875, and then incremented at step880. At step 885, one or more uplink and downlink resource blocks areassigned to feeder terminal I for hypothesised global schedule n, havingregard to the controllability matrix. Thereafter, at step 890, a MIMOmode is assigned for each resource block used for feeder terminal I ofthe hypothesised global schedule n, and then similarly at step 892 atransmit PCM value is assigned for each resource block used for feederterminal I of hypothesised global schedule n.

At step 894, it is determined whether I is less than L, where asdiscussed earlier L denotes the number of feeder terminals. If it does,then the inner loop is repeated beginning at step 880. However, if atstep 894 it is determined that I is not less than L, then the processproceeds to step 896, where it is determined whether n is less than N,as discussed earlier N being the number of hypothesised global schedulesto be used by the evolutionary algorithm. If it is, then the outer loopis reiterated by returning to step 870. If it is not, then thisindicates that all of the hypothesised global schedules have beenproduced, and accordingly the process proceeds to step 898 where theinitialisation of the set of hypotheses is considered completed.

Evaluate Links

In accordance with step 815 of FIG. 28, every FT/FBS link within eachhypothesis is evaluated. This phase is highly parallelised and may beimplemented in a distributed fashion. During this phase, whileconsidering the co-channel interference, the MIMO channel capacity forevery link in the network is computed. The capacity is measured in bitsper second per Hz and takes into account all implementation losses. Theimplementation losses are calculated at the FTs and communicated at theassociated FBSs. Additional measures may be computed, for example, theround trip delay per link. This measure could play an important part intraffic routing when relays are added to the network.

FIG. 30 illustrates the steps for evaluating the links. In summary, foreach FT, the UL and DL MIMO capacities are evaluated. Parallelisation isindicated by the asterisk in the figure. It should be noted that thevisibility matrix is obtained from the network parameter database, andis used to identify relevant co-channel interferers.

Considering FIG. 30 in more detail, at step 900, the process starts,whereafter at step 905 the set of input hypotheses, the number of feederterminals in the system, and the visibility matrix are obtained from thenetwork parameters 910 stored in a database such as the database 780 ofFIG. 27. Thereafter, at step 915, a variable I is set equal to 0, and isthen incremented at step 920. At step 925, the uplink and downlink Rvalues are updated for all hypotheses. The visibility matrix is referredto during this process, as the visibility matrix identifies for each FTwhich FBS communications it can observe. Step 925 can be performed inparallel, due to the separate nature of the individual hypotheses in theset.

At step 930, the uplink and downlink capacities and LQIs are evaluatedfor feeder terminal I, again across all hypotheses. As with step 925,this process can be highly parallelised, given the separate nature ofthe individual hypotheses.

At step 935, it is determined whether the variable I is less than thetotal number of FTs, and if so, the process loops back to step 920.However, when it is determined at step 935 that the variable I is nolonger less than the number of FTs, and accordingly all FTs have beenanalysed, then the process proceeds to step 940, where the evaluatelinks process is considered complete.

Evaluate Hypotheses

Here each hypothesis H_(n) is awarded a score r_(n). As a rule, thehigher the score the better. For each link, the channel capacity perlink is converted to throughput (bits per second) by considering thenumber of resources block allocations for each frame. The throughput perlink is checked against the target throughput. A reward is thenallocated to each link. The reward, which is a positive value, is afunction of the offered throughput and the desired throughput. Anexample reward function is given in FIG. 31A. In FIG. 31A, no reward isallocated if the offered traffic in a link is less than the desiredthroughput. A maximum reward is allocated to a link if the target ismet. A diminishing reward is applied if the offered traffic far exceedsthe target throughput. Throughput targets are time and locationdependent. That is, a certain link may demand different amounts oftraffic depending on the time of day. Furthermore, it may also beexpected that business districts will be heavily loaded during the dayand lightly loaded during the night or during public holidays; thereverse may be true in suburban areas.

An additional reward is allocated to each link depending on the numberof resource blocks used for delivering the traffic. An example functionis illustrated in FIG. 31B, where the reward is maximised if oneresource block (subchannel/slot) is used.

A further reward may be allocated to each link by considering the roundtrip delays. Again a candidate reward function may be an exponentialdecaying function (similar to FIG. 31B) where short delays are rewardedthe most, and long round trip delays yield little or no reward.

For each link, the throughput reward, the resource utilisation rewardand the round trip delay reward are added (a weighted average mayinstead be used if desired) to yield the total reward for that link.

For each hypothesis, the vector of (total) rewards is mapped to a singlescalar that determines the overall fitness value of the hypothesis.There are a number of mapping functions, for example:

-   -   Mean (arithmetic or harmonic): this yield an average fitness        value    -   x^(th) percentile: (for example the 5^(th) percentile) that        ensures (100-x) percent of links have the same or better fitness        value    -   min: returns the fitness value of the worst link.

The vector to scalar mapping can be done in multiple steps. For example,the vector reward values for all links associated with an FBS may bemapped to a scalar, and then the scalar output for all FBSs may in turnbe mapped to a single scalar to reflect the overall fitness assignmentfor each hypothesis.

FIG. 32 is a flow diagram illustrating how the above evaluation processis performed in one embodiment. At step 950, the evaluation processbegins, whereafter at step 952, the number of hypothesised globalschedules, the number of FTs and the number of FBSs are obtained fromthe network parameters 954 in the database 780.

At step 956, the variable I is set equal to 0, whereafter at step 958 Iis incremented. Then, at step 960 the uplink and downlink reward forfeeder terminal I is evaluated across all hypotheses. This process isperformed in parallel, due to the discrete nature of the differenthypotheses. Thereafter, at step 962, it is determined whether thevariable I is less than the number of FTs, and if so the process returnsto step 958. However, when it is decided at step 962 that the variable Iis no longer less than the number of FTs, then at this point the uplinkand downlink rewards for all feeder terminals across all hypotheses iscomplete, and the process proceeds to step 964.

Steps 964, 966, 968 and 970 perform the same process as steps 956, 958,960, 962, but in respect of each FBS rather than each FT. Again, step968 can be performed in parallel for all hypotheses. Once it isdetermined at step 970 that all FBSs have been considered, then theprocess proceeds to step 972.

At step 972, a variable n is set equal to 0 and then at step 974 n isincremented. Thereafter, at step 976 the various uplink and downlinkrewards for hypothesis n are evaluated in order to produce a rewardvalue for the hypothesis. At step 978, it is determined whether allhypotheses have been considered, and if not the process returns to step974. However, once it is determined at step 978 that all hypotheses havebeen considered, then the process proceeds to step 980 where theevaluation process is considered complete.

Select Hypothesis

The selection performed at step 825 of FIG. 28 is done in a randomfashion, selecting the hypotheses with high rewards more often. As aconsequence, hypotheses with low rewards will eventually be discardedand those with high values will proceed to the next stage. If N denotesthe number of (input) hypotheses that enter the selection process, thenN will also be the number of (output) hypotheses that will be generatedby the selection process. It should be clear that some output hypotheseswill be in duplicate.

FIG. 33 illustrates the steps performed in one embodiment in order toselect a modified set of hypotheses. At step 1000, the process begins,whereafter at step 1005 the number of hypothesised global schedules N isobtained, and then the number of highest ranked hypotheses K isdetermined with reference to the results of the evaluation processdescribed with reference to FIG. 32, this information being stored asnetwork parameters 1010 within the database 780.

At step 1015, the K highest ranked hypotheses are selected, whereafterat step 1020 a further N-K hypotheses are selected randomly. Thereafter,at step 1025, the selection process is considered complete, and theresultant modified set of hypotheses are output.

In practice, the value K is typically equal to one or two. The selectionof the K highest ranked hypotheses guarantees the survival of the bestsolution.

Generate a New Set of Hypotheses

After the modified set of hypotheses has been produced by step 825 ofFIG. 28, a replacement set of hypotheses is created by the reproductionstep 835 of FIG. 28. If N denotes the number of (input) hypotheses thatenter this process, then N will also be the number of new (output)hypotheses that will be generated.

This phase contains the following four operations, described for examplein the earlier mentioned publication Weise T., “Global OptimizationAlgorithms, Theory and Application”,http://www.it-weise.de/projects/book.pdf.

-   -   Creation: One or more hypotheses are generated with random        attributes.    -   Duplication: One or more input hypotheses with the highest score        are copied without any modifications.    -   Mutation: A minor attribute of an input hypothesis is randomly        modified to generate a new hypothesis. The selected input        hypotheses for this stage are selected in a random fashion.    -   Recombination (or Crossover): Attributes from pairs of input        hypotheses are randomly swapped to create pairs of new        hypotheses. The selected input hypotheses for this stage are        selected by random.    -   In one embodiment, a fifth new operation is also added:    -   Reincarnation: Reinstate one or more global schedules (stored in        a database). For example, reinstate a global schedule that was        applied 24 h and/or 7 days ago. The assumption here is that        traffic demand is cyclostationary.

Let N_(C), N_(D), N_(M), N_(R), and N_(I), denote the number ofcreations, duplications, mutations, recombinations and reincarnations,respectively. It will be clear that N=N_(C)+N_(D)+N_(M)+N_(R)+N_(I). Inone embodiment, N_(c) is typically set to 1; random starting points aregenerally a good idea to avoid local minima during optimisation. N_(D)is typically set to 2 ensuring the survival of the fittest. The numberof recombination N_(R) is by design an even number and usually does notexceed the number of mutations N_(M).

During a mutation or a recombination one or more attributes of thehypotheses are modified. This is carried out by modifying or appendingone of the following:

-   -   1. Resource block assignment (use an alternative, add a new one,        or delete one),    -   2. MIMO mode    -   3. TX Precoding matrix mode

For any mutation or recombination it must be ensured that the changesresult in valid entries. For example, resource block assignments must beorthogonal for all FTs connected to the same FBS.

FIG. 34 illustrates the steps for generating a new set of hypotheses.

At step 1050, the generation step begins, whereafter at step 1055 theset of input hypotheses are obtained from the network parameters 1060along with a set of previously optimised hypotheses, for examplehypotheses that are considered to provide particularly good solutionshaving regard to a particular time of day, day of the week, etc. Thevariables N_(C), N_(D), N_(M), N_(R), and N_(I) are also obtained, thesevalues typically having been set in advance. Thereafter, at step 1065,N_(C) random hypotheses are created, and at step 1070 the best N_(D)hypotheses from the set of input hypotheses are duplicated. At step1075, N_(M) hypotheses from the set of input hypotheses are mutated,with the hypotheses selected for this process typically being random. Atstep 1080, N_(R) hypotheses from the set of input hypotheses aresubjected to the recombination process. Again, the hypotheses chosen forthis process are typically random, other than the requirement for aneven number of hypotheses to be chosen. At step 1085, N_(I) hypothesesare reinstated from the set of previously optimised hypotheses,whereafter the generation process is considered complete at step 1090.

It will be appreciated that the various parameters N_(C), N_(D), N_(M),N_(R), and N_(I) can be varied if desired. For example, whilst at sometimes of the day, it may be appropriate to reinstate an hypothesis froma set of previously optimised hypotheses at step 1085, there may beother times of day when this is not appropriate, and accordingly itwould be appropriate to set the variable N_(I) to 0 and to adjust theother variables accordingly.

Apply Preferred Global Schedule

This procedure (step 830 of FIG. 28) is responsible for selecting theglobal schedule and disseminating the information to the various nodesof the network. Specifically, the FNC searches through the current setof hypotheses and selects the one yielding the highest score. Theselected hypothesis will thus be the next global schedule to be appliedto the network. The FNC is also responsible for communicating the globalschedule to its connected FBSs. In order to minimise the amount ofinformation sent to each FBS, the FNC will communicate portions of theglobal schedule pertinent to each FBS.

FIG. 35 is a flow diagram illustrating the above process. At step 1100,the process starts, whereafter at step 1105 the set of input hypothesesis obtained. At step 1110, the best hypothesis from the set, based onits current reward value, is selected, and then at step 1115 theselected hypothesis is set as the next global schedule. Thereafter, atstep 1120, the global schedule is distributed to the FBSs and FTs,whereafter the process is considered completed at step 1125.

In the above described embodiment, it is assumed that a single feedernetwork controller manages all of the FBSs and FTs. However, in analternative embodiment, it is possible to distribute this task amongstmultiple feeder network controllers, as for example illustrated in FIG.36A. In particular, from a comparison of FIG. 36A with FIG. 5A, it willbe seen that the number of FBSs and FTs are unchanged, and theindividual controllability regions of each FBS 161 to 168 is alsounchanged (namely the regions 171 to 178). However, the various FBSs arenot all controlled by a single FNC and instead FNC 1150 controls theFBSs 161, 162, 163, the FNC 1160 controls the FBSs 164, 165 and the FNC1170 controls the FBSs 166, 167, 168. Accordingly, in this embodiment,not only are there controllability regions for each FBS, defining theFTs controlled by that FBS, but there are also now separatecontrollability regions for each FNC, defining the FBSs within thecontrol of each FNC. Accordingly, the FNC 1150 has the associatedcontrollability region 1155, the FNC 1160 has the associatedcontrollability region 1165, and the FNC 1170 has the associatedcontrollability region 1175. Accordingly, the following twocontrollability matrices can be formed:

FBS/FT controllability matrix (C1): this is a sparse matrix populatedprimarily with zeros. The rows of C1 correspond to the FTs and thecolumns to the FBSs. A one in the i^(th) row and the j^(th) columnindicates that the FT_(i)-FBS_(j) pair is connected (i.e. an actualfeeder link exists between them). Thus, data and control messages aredelivered in the UL and the DL for the FT_(i)-FBS_(j) pair.

FNC/FBS controllability matrix (C2): this is again a sparse matrixpopulated primarily with zeros. The rows of C2 correspond to the FBSsand the columns to the FNCs. A one in the i^(th) row and the j^(th)column indicates that the FBS_(i)-FNC_(j) pair is connected, and FNC, isresponsible for the delivery and reception of data and control messagesto FBS_(i).

The visibility regions are also defined, which are specified by thevisibility matrix (V): The rows of the visibility matrix correspond tothe FTs and the columns to the FBSs. A one in the i^(th) row and thej^(th) column indicates that the FT_(i)-FBS_(j), pair may communicate orinterfere with each other; a zero indicates that the FT-FBS pair cannotcommunicate or interfere with one another. These visibility regions 181to 188 are shown in FIG. 36B, and are unchanged from those shown in FIG.5B.

During the deployment of the FBSs in the network, each FBS is allocated(for example manually) to an FNC. The matrix C2 is completely specifiedafter the deployment stage. Following the FT deployment, the soundingprocess yields the matrix V. The FNC responsible for global soundingwill determine the initial FBS/FT controllability matrix C1. The initialFBS/FT assignment may for simplicity be based on the carrier ReceivedSignal Strength Indicator (RSSI), which is a wideband measure primarilyaffected by path loss and shadow fading.

C1 (or C2) is a valid matrix, if the sum of each rows of C1 (or C2) isequal to one. Assuming equal loading across the network, it isreasonable to assume that each FBS (or FNC) is connect to theapproximately the same number of FTs (of FBSs). Thus, the column sums ofC1 (or C2) should be approximately the same. While any valid matrix forC2 is acceptable as an initial setting, C1 must satisfy the followingrule: C1=C1.*V1. Here the operator (.*) denotes element wisemultiplication. The rule ensures that the FBS/FT controllability regionsare a subset of the visibility regions.

The steps for computing and applying global schedules in the multi-FNCcase generally follow the single FNC case described earlier withreference to FIG. 28. FIG. 37 illustrates the general process performedacross multiple FNCs. Accordingly it can be seen that FNC 1 performs thesteps 1200 to 1235, which correspond generally with the steps 800 to 835of FIG. 28. Similarly, FNC 2 performs the steps 1300 to 1335, whichagain correspond generally with steps 800 to 835 of FIG. 28.

In one embodiment, when initialising the set of hypotheses in eachindividual FNC, each FNC has regard to its specific controllabilitymatrix given by the combination of C1 and C2. Considering the earlierdescribed FIG. 29, this then involves the additional step between steps880 and 885 of determining whether the feeder terminal I resides withinthe controllability matrix specific to that FNC. If it does, then steps885, 890 and 892 are performed, whereas if not the process just branchesdirectly to step 894. It will be appreciated that by this process, inthe initialised set of hypotheses in each FNC, each hypothesised globalschedule will be only partly completed.

However, at any point in time the distribution of the global schedule iscontrolled by one of the FNCs holding a valid token. During the startupphase this setup will simply force traffic through the part of thefeeder network associated with the FNC holding the token. However, aswill be discussed in more detail later with reference to FIG. 38, thetoken is passed over time between the various FNCs, and as a result thesize of the active network at any point in time will further expand tocover the previous FNC controllability region(s) plus thecontrollability region of the current FNC. Assuming the token is passedrelatively frequently during the startup phase, then this will ensurethat the entire network will be up and running very quickly and that theset of hypotheses being considered independently by each FNC willrapidly become fully populated.

With regard to the evaluation of links step described earlier withreference to FIG. 30, the process of FIG. 30 can be appliedindependently in each FNC. In one embodiment, for any unfilled entry inan input hypotheses, a reward value of 0 will be applied. Over time thiswill ensure that the more completed global schedules achieve higherrewards, displacing only partly completed global schedules. The step ofevaluating the set of hypotheses as described earlier with reference toFIG. 32 can again be applied independently in each of the FNCs in orderto produce overall rewards for each hypothesis. Similarly, the step ofselecting a set of hypotheses described earlier with reference to FIG.33 can again be applied independently in each FNC. Further, the step ofgenerating a new set of hypotheses as described earlier with referenceto FIG. 34 can be applied independently in each FNC. However, in oneparticular embodiment, the steps 1065, 1075 and 1080 will be performedsuch that any particular FNC only alters entries of the hypotheses thatare within its associated controllability region as given by thematrices C1 and C2.

As shown in FIG. 37, the process of applying a preferred global scheduleinvolves some inter-FNC communication as indicated by the line 1340. Inparticular, within each FNC, the step of applying the global schedule inone embodiment follows the process shown in FIG. 38.

The process starts at step 1350, whereafter at step 1355 each FNC getsits associated set of input hypotheses. It is then determined whetherthe FNC performing the process has the token in its possession at step1360. If it does, then steps 1375, 1380 and 1385 are followed, thesecorresponding with the earlier described steps 1110, 1115 and 1120 ofFIG. 35, but with the global schedules being broadcast to the other FNCsat step 1385 rather than directly to the FBSs and FTs.

If it is determined at step 1360 that the token is not in the possessionof the FNC, then the process proceeds to step 1365, where that FNC getsthe global schedule H_(m), this being the global schedule that has beenbroadcast by the FNC that is in possession of the token. In addition tousing that broadcast global schedule as the current global schedule, atstep 1370 the FNC will also incorporate that global schedule into itsset of hypotheses. One simple approach to achieve this would be to swapout randomly one of its current hypotheses and replace it by thebroadcasted global schedule received at step 1365.

Assuming the FNC does have the token in its possession, and accordinglyhas performed steps 1375, 1380 and 1385, it is then determined at step1390 whether the token has expired. If it has, then the token is sent toanother FNC at step 1392. Various schemes can be used to decide whichFNC to send the token to, but in a simple scheme a round-robin approachis adopted, so that each FNC is responsible for managing the globalschedule in turn.

When the process proceeds to step 1394, the current global schedule isdistributed to the connected FBSs and FTs. In order to minimise theamount of information sent “over the air” to each FBS, the FNCs willcommunicate portions of the global schedule that are pertinent to eachFBS/FT. Each individual FNC will decide the relevant information basedon the controllability matrices C1 and C2. Following step 1394, the stepof applying the global schedule is considered complete at step 1396.

By employing multiple feeder network controllers, improved performancecan be realised, since the evolutionary algorithm is applied in parallelacross multiple feeder network controllers, enabling a fasterconvergence upon a good solution for an updated global schedule havingregard to observed or anticipated traffic loading.

In addition to the above discussed global schedules which a feedernetwork controller can compute and communicate to the FBSs, in someembodiments the feeder network controller is configured to provide eachFBS with an “autonomous schedule”. As previously discussed, globalschedules for the network are centrally determined by the FNC, seekingto attain high spectral efficiency by providing highly-optimisedphysical-layer allocations for every FBS-FT link. However, whilst aglobal schedule may be regularly updated by the FNC, for any specificphysical-layer frame the schedule is fixed network-wide. Furthermore,given the computation requirements associated with generating a globalschedule, it is expected that updates to the global schedule may occurin a timescale of, say, every few seconds. As such, situations may arisein which the time required to update a global schedule may be too longto respond to rapidly changing network demand. For example, in order tomaintain an acceptable quality of service (QoS) for voice datatransmission, response times of the order of tens of milliseconds may berequired when the bandwidth requirements of particular links in thenetwork are changing rapidly. In such a situation an autonomousschedule, which provides each base station with the ability to scheduleits own traffic may be more appropriate.

In general a “schedule” consists of control information indicating howthe available resource blocks are to be used and network interferenceinformation associated with each resource block. In the case of a globalschedule (as discussed above), the following components are specified(in addition to an indication of whether the schedule corresponds touplink (UL) or downlink (DL) transmission:

-   -   1. Resource Block (RB) assignment, indicated by a FBS ID, FT ID        and a resource block ID;    -   2. Multiple Input Multiple Output (MIMO) mode, specifying the        multi-antenna transmission scheme;    -   3. Transmit Precoding Matrix (TX PCM), instructing the        operations to map data streams onto antenna ports;    -   4. Receive Antenna Selection (RX AS), indicating one or more RX        antennas to be used;    -   5. Link Quality Indicator(s)—one or more (depending on the MIMO        mode) data stream quality measures; and    -   6. R_(r,n)—a covariance matrix of the interference as seen by        the receiver n on RB index r.

In the case of an autonomous schedule, essentially the same parametersare provided, except that the RB assignment may now specify a number ofFT IDs, indicating that the specified FBS is being granted the abilityto use this RB to establish a link with any one of these specified FTs.Furthermore, the above-listed six parameters are supplemented in anautonomous schedule by a seventh parameter:

-   -   7. RU—a resource utilisation fraction, telling the FBS the        probability of using the specified RB.

This resource utilisation fraction (RU) is a function of the number ofresource blocks available and the traffic intensity, and can range froma small value up to the maximum of 100%. In other words, when schedulingits own traffic according to the autonomous schedule the FBS selectsfrom the RBs available for establishing a link to a particular FT inaccordance with the RU values associated with each RB.

Given the probabilistic nature of the selection of RBs by the FBSs toestablish its links and since the autonomous schedules are designed tocarry fast-rate, time-varying traffic, it is not possible to preciselydetermine (and therefore minimise) the intercell interference. Insteadan approach is taken which seeks to keep such intercell interference atan acceptable level. The mitigation of intercell interference in theautonomous regions is carried out by: i) interference avoidance, and ii)interference averaging.

i) Interference avoidance is carried by resource partitioning. The RBsin the autonomous region may be subdivided into sets of disjoint RBallocations. A collection of RBs belonging to the same set is called a“group”. For example, a re-use 3 partitioning scheme will divide theentire autonomous region into three groups. In this example each groupwill be associated with a unique channel (RB). Initially, for uplinktransmission, the allocation of a FT to a group will be done byconsidering the visibility regions. FTs in the same visibility regionsare selected in a round-robin fashion and randomly assigned to one ofthe available groups. A similar procedure then follows for the downlinktransmission. Further refinement of the FT/RB association may be doneusing some well known techniques (see, for example: M. Döttling, W. Mohrand A. Osseiran, Radio Technologies and Concepts for IMT-Advanced,Wiley, 2009, pp. 360-365), such as Soft Frequency Reuse (SFR),Fractional Frequency Reuse (FFR), or scheduling techniques based on acost function that includes the interference, path loss and data ratesachieved by each receiver.

ii) Interference averaging is accomplished within the autonomousschedule by randomising the physical layer accesses (i.e. the selectionof RB) across frequency and in time. The reliability of the transmittedsignals is ensured by well established wireless communication techniquessuch as Forward Error Correction (FEC), and Hybrid Automatic RepeatRequest (H-ARQ). In addition, and most importantly, the FNC alsospecifies an expected interference covariance matrix which takes intoaccount the probability of co-channel interference generated by otherFBS-FT links in the same autonomous region. Thus a probabilisticapproach is taken to the expected co-channel interference. Whilst inthis preferred embodiment the resource utilisation fractions are used asa selection probability when selecting between the resource blocks, in avariant the interference averaging in the autonomous schedule may alsobe achieved by selecting from said resource blocks such that within apredetermined time period usage of said resource blocks corresponds tosaid resource utilisation fractions. According to this variant, theallocation of the resource blocks for a given link may for example beperformed in a simple round robin fashion, but wherein the resourceblocks available for each selection is determined by the need to complywith the resource utilisation fractions in the predetermined timeperiod. For example, to provide a given link any appropriate resourceblock may be initially selected, but as the predetermined time periodelapses, the resource blocks available may be biased such that usage ofresource blocks evolves towards the resource utilisation fractions.

FIG. 39 schematically illustrates the basic steps involved in generatingan autonomous schedule in a feeder network controller for distributingto the network. At step 1500 the process is started, where the FNCreceives sounding data from the network. This sounding data can yieldvarious channel metrics that include (but are not limited to): channelimpulse responses, complex channel frequency responses, frequencydependent co-variance matrices of the received signals, frequencydependent eigenmodes, and so on. Essentially these channel metricsprovide a system-wide view of the quality of the wireless channels inuse.

Next at step 1502 the FNC receives traffic reports from the network.These traffic reports provide the FNC with detailed information aboutthe network traffic currently being handled, and in particular how theloading of that network traffic is distributed across the various linksthat comprise the network.

On the basis of the information received at steps 1500 and 1502, at step1504 the FNC determines a metric for each link. This metric gives theFNC an indication of the current quality of each link (for example thismay be an indication of a current rate of packet loss or a currentaverage packet delay, or conversely it may be an indication of thethroughput on that link). Having determined the metric for each link, atstep 1506 the FNC determines the resource allocation fraction (RU)values, seeking to optimise the links under consideration. For example,the FNC may adjust the RU values such that the rate of packet loss doesnot exceed a predefined maximum level.

Then, on the basis of these RU values, at step 1508 the FNC determinesthe other autonomous schedule parameters, in particular determining theco-channel interference matrices R_(r,n) and at step 1510 the autonomousschedule is distributed to the network.

FIG. 40 schematically illustrates the configuration of a feeder networkcontroller in this embodiment. Feeder network controller 1550 containsautonomous schedule computation circuitry 1552 for determining resourceutilisation fractions, for determining co-channel interference matricesand for generating autonomous schedules. Via the input interface 1554,the autonomous schedule computation circuitry receives sounding datafrom the network which provides information about the quality of thelinks in use. Via the input interface 1556, the autonomous schedulecomputation circuitry 1552 receives traffic reports from the networkindicating how the network traffic currently being handled isdistributed across the links in the network.

The autonomous schedule computation circuitry 1552 itself comprises ametric determination unit 1558 which is configured to determine thequality of each link on the basis of the received traffic reports. Theschedule computation circuitry 1552 also comprises resource utilisationcomputation unit 1560, which determines the resource allocation fraction(RU) values, seeking to optimise the links under consideration. These RUvalues are passed to the interference computation unit 1562, whichdetermines the co-channel interference matrices R_(r,n) in aprobabilistic fashion on the basis of the RU values. Finally, uplink anddownlink autonomous schedules are prepared for distribution in theschedule preparation unit 1564 in which the full parameters required todefine each schedule are collated. The autonomous schedules are passedto the network from autonomous schedule computation circuitry 1552 viadistribution interface 1570. Autonomous schedule computation circuitry1552 also has access to a database 1572, in which previous schedules,traffic reports, sounding data and so on can be stored for futurereference, and from which previously stored schedules, parameters, dataand so on can be retrieved. Finally, feeder network controller 1550 alsohas an FNC-to-FNC interface 1574 enabling it to exchange data with otherfeeder network controllers.

FIG. 41 illustrates an example arrangement of FBSs and FTs during anuplink schedule, showing how a determined set of co-channel interferencematrices for these network components (which takes into account thecorresponding resource utilisation (RU) fractions) may determine aselected reception beam shaping to be applied to one of the FBS (in thiscase FBS 1). The arrangement illustrates four FBSs and four FTS, which(purely for the sake of clarity of explanation here) are configured inthis uplink schedule such that FT 1 transmits to FBS 1, FT 2 transmitsto FBS 2, FT 3 transmits to FBS 3 and FT 4 transmits to FBS 4.

However, due to the fact that all four of these transmissions areconfigured to be provided by links which may be established using thesame RB, the co-channel interference experienced by each FBS whenreceiving its uplink transmission needs to be taken into account. Thefigure is illustrated from the point of view of FBS 1, which isreceiving an uplink transmission from FT 1, but may experienceco-channel interference due to the simultaneous uplink transmissionsgenerated by FT 2, FT 3 and FT 4. Note in particular that for the RBunder consideration, the FT 2-FBS 2 link is allocated an RU of 90%, theFT 3-FBS 3 link is allocated an RU of 20%, and the FT 4-FBS 4 link isallocated an RU of 10%. Given these values, and other parameters such asthe relative distances from FBS 1 of the other FTs and informationderived from channel sounding, a co-channel interference matrix has beendetermined for FBS 1. In particular this co-channel interference matrixindicates that the most significant source of co-channel interferencefor FBS 1 during this uplink schedule using this RB is FT 2.

On the basis of the expected co-channel interference matrix, FBS 1 isconfigured to apply beam weighting to its multiple antenna, to shape thebeam pattern in its reception configuration. Hence, one of the nulls ofthe beam pattern is arranged to be pointed directly at FT 2 to suppressthat source of co-channel interference. The other null of the beampattern is arranged to be pointed somewhere between FT 3 and FT 4, sincethis has been found to give the best co-channel interference suppressionthat can be attained with only two nulls. A more complex antenna whichcould be beam weighted in a more sophisticated manner could of coursedirect nulls at each of the interfering FTs in the illustrated example.

FIG. 42 illustrates how, for a limited number of links (namely betweenone FBS and three FTs) the resource utilisation fractions aredistributed across the orthogonal resource blocks. The figure shows anexample autonomous schedule determined for use within the networkillustrated in 17. Here the autonomous schedule is determined for FBS₂to schedule the network traffic it exchanges with FT₁₁, FT₁₂ and FT₁₃.As can be seen in the figure, the upper five frequency rows do not formpart of the autonomous schedule (all RBs being allocated a zero RUvalue), whilst the lower 4 frequency rows show the allocated RU valuesfor FT₁₁, FT₁₂ and FT₁₃ respectively. Hence FBS₂ is able to use theselower 4 frequency rows to allocate to its own network traffic asrequired, and is therefore able to respond faster to short term localvariations in network usage than would be the case if these resourceblocks belonged to a global schedule.

From the above description of embodiments, it will be appreciated thatthe wireless feeder network of such embodiments provides an efficientwireless backhaul, which can be used to access base stations in caseswhere the provisioning of wired backhaul would be uneconomic. A typicalscenario where the wireless feeder network would be useful would be in adense urban deployment where pico base stations are deployed on streetfurniture. The pico base station provides much needed capacity andcoverage enhancements, and by eliminating the need for wired backhaul,use of the wireless feeder network has the potential to reduce ongoingoperational expense (OPEX). By employing the above described techniquesof embodiments, it is ensured that the spectrum is used sparingly in thewireless feeder network, thereby maximising the amount of spectrumavailable for the access network.

In one embodiment, the wireless feeder network operates in the same bandas the access layer. This allows the operator to deploy a pico basestation style of network within the constraints of a single RF spectrumlicense. In accordance with embodiments, it is possible to achieve anaverage spectral efficiency greater than 10 bits per second per Hertz.This can be achieved within a single frequency network, and enablespreservation of spectrum for the access layer.

The wireless feeder network may be deployed in either in-band orout-of-band modes. In-band operation means that the feeder transmissionsare multiplexed to operate within the same radio channel as the accesslayer. Out-of-band operation means a different RF channel may be used,adjacent, non-adjacent or in a completely different RF band to theaccess layer channel(s).

The wireless feeder network may be deployed in either TDD or FDD modes.TDD is primarily required for compatibility with mobile WiMAX, and FDDwith LTE.

Although particular embodiments have been described herein, it will beappreciated that the invention is not limited thereto and that manymodifications and additions thereto may be made within the scope of theinvention. For example, various combinations of the features of thefollowing dependent claims could be made with the features of theindependent claims without departing from the scope of the presentinvention.

We claim:
 1. A method of controlling a wireless network for connectingnetwork users to a communications network, the wireless networkcomprising a plurality of network components, the network componentscomprising a plurality of base stations connected to the communicationsnetwork and a plurality of terminals connected to the network users,each terminal having a link with a base station to form a basestation/terminal pair, and the links being established over a wirelessresource comprising a plurality of resource blocks, the methodcomprising the steps of: determining, for each base station/terminalpair, a set of resource utilisation fractions, said set of resourceutilisation fractions indicating probabilities for establishing saidlink between that base station and that terminal via each of saidplurality of resource blocks; determining a set of co-channelinterference matrices, a co-channel interference matrix being determinedfor each network component, said co-channel interference matrixindicative of an expected interference from other network components,for each of said plurality of resource blocks, when that networkcomponent receives network traffic via that resource block, wherein saidexpected interference is probabilistically determined in dependence onsaid sets of resource utilisation fractions; distributing, to each basestation, corresponding elements from said sets of resource utilisationfractions and from said sets of co-channel interference matrices;suppressing, in each network component, co-channel interference independence on the co-channel interference matrix determined for thatnetwork component; and in each base station, when exchanging networktraffic with said plurality of terminals, dynamically establishing saidlinks as required to handle said network traffic for that base stationby selecting from said resource blocks in accordance with said resourceutilisation fractions.
 2. The method as claimed in claim 1, wherein saiddynamically establishing said links comprises selecting from saidresource blocks according to probabilities given by said resourceutilisation fractions.
 3. The method as claimed in claim 1, wherein saiddynamically establishing said links comprises selecting from saidresource blocks such that within a predetermined time period usage ofsaid resource blocks corresponds to said resource utilisation fractions.4. The method as claimed in claim 1, further comprising the step, priorto said step of determining, for each base station/terminal pair, saidset of resource utilisation fractions, of: determining a metric for eachlink, said metric indicative of a current quality of that link, andwherein said sets of resource utilisation fractions are determined independence on said metrics.
 5. The method as claimed in claim 4, whereinsaid metric comprises a packet loss measurement.
 6. The method asclaimed in claim 4, wherein said metric comprises a packet delaymeasurement.
 7. The method as claimed in claim 4, wherein said metriccomprises a link throughput measurement.
 8. The method as claimed inclaim 4, wherein said step of determining, for each basestation/terminal pair, a set of resource utilisation fractions comprisesadjusting said resource utilisation fractions to reduce a differencebetween said metric determined and a target metric for each link.
 9. Themethod as claimed in claim 1, wherein said suppressing co-channelinterference comprises arranging a beam pattern at that networkcomponent to suppress the co-channel interference during reception. 10.The method as claimed in claim 1, wherein said suppressing co-channelinterference comprises applying beam weights to a multi-element antenna.11. The method as claimed in claim 1, further comprising the step, priorto said step of determining, for each base station/terminal pair, saidset of resource utilisation fractions, of: receiving traffic reportsfrom the wireless network, said traffic reports indicative of previoususage of said links, and wherein said sets of resource utilisationfractions are determined in dependence on said traffic reports.
 12. Themethod as claimed in claim 1, further comprising the step, prior to saidstep of determining, for each base station/terminal pair, said set ofresource utilisation fractions, of: receiving sounding data from thewireless network, said sounding data indicative of visibility betweensaid network components, and wherein said sets of co-channelinterference matrices are determined in dependence on said soundingdata.
 13. The method as claimed in claim 1, further comprising the step,prior to said step of determining, for each base station/terminal pair,said set of resource utilisation fractions, of: receiving expectedtraffic information, said expected traffic information indicative of anexpectation of usage of said links, and wherein said sets of resourceutilisation fractions are determined in dependence on said expectedtraffic information.
 14. A method as claimed in claim 1, wherein saidwireless network is a wireless feeder network, said plurality of basestations comprises a plurality of feeder base stations and saidplurality of terminals comprises a plurality of feeder terminals.
 15. Amethod as claimed in claim 1, wherein said resource blocks are formed bydividing the wireless resource in both the frequency and time domains.16. A method as claimed in claim 1, wherein said base stations andterminals are at fixed locations.
 17. A wireless network controller forcontrolling a wireless network which connects network users to acommunications network, the wireless network comprising a plurality ofnetwork components, the network components comprising a plurality ofbase stations connected to the communications network and a plurality ofterminals connected to the network users, each terminal having a linkwith a base station to form a base station/terminal pair, and the linksbeing established over a wireless resource comprising a plurality ofresource blocks, the wireless network controller comprising: a resourceutilisation fraction computation circuitry for determining, for eachbase station/terminal pair, a set of resource utilisation fractions,said set of resource utilisation fractions indicating probabilities forestablishing said link between that base station and that terminal viaeach of said plurality of resource blocks; co-channel interferencematrix computation circuitry for determining a set of co-channelinterference matrices, a co-channel interference matrix being determinedfor each network component, said co-channel interference matrixindicative of an expected interference from other network components,for each of said plurality of resource blocks, when that networkcomponent receives network traffic via that resource block, wherein saidexpected interference is probabilistically determined in dependence onsaid sets of resource utilisation fractions; and a distributioninterface for distributing, to each base station, corresponding elementsfrom said sets of resource utilisation fractions and from said sets ofco-channel interference matrices, wherein said co-channel interferencematrix computation circuitry is configured to determine said co-channelinterference matrices to cause the suppression, in each networkcomponent, of co-channel interference in dependence on the co-channelinterference matrix determined for that network component, and whereinsaid resource utilisation fraction computation circuitry is configuredto determine said resource utilisation fractions such that, in each basestation, when exchanging network traffic with said plurality ofterminals, said links are dynamically establishing as required to handlesaid network traffic for that base station by selecting from saidresource blocks in accordance with said resource utilisation fractions.18. A wireless network controller for controlling a wireless networkwhich connects network users to a communications network, the wirelessnetwork comprising a plurality of network components, the networkcomponents comprising a plurality of base stations connected to thecommunications network and a plurality of terminals connected to thenetwork users, each terminal having a link with a base station to form abase station/terminal pair, and the links being established over awireless resource comprising a plurality of resource blocks, thewireless network controller comprising: resource utilisation fractioncomputation means for determining, for each base station/terminal pair,a set of resource utilisation fractions, said set of resourceutilisation fractions indicating probabilities for establishing saidlink between that base station and that terminal via each of saidplurality of resource blocks; co-channel interference matrix computationmeans for determining a set of co-channel interference matrices, aco-channel interference matrix being determined for each networkcomponent, said co-channel interference matrix indicative of an expectedinterference from other network components, for each of said pluralityof resource blocks, when that network component receives network trafficvia that resource block, wherein said expected interference isprobabilistically determined in dependence on said sets of resourceutilisation fractions; and a distribution interface means fordistributing, to each base station, corresponding elements from saidsets of resource utilisation fractions and from said sets of co-channelinterference matrices, wherein said co-channel interference matrixcomputation means is configured to determine said co-channelinterference matrices to cause the suppression, in each networkcomponent, of co-channel interference in dependence on the co-channelinterference matrix determined for that network component, and whereinsaid resource utilisation fraction computation means is configured todetermine said resource utilisation fractions such that, in each basestation, when exchanging network traffic with said plurality ofterminals, said links are dynamically establishing as required to handlesaid network traffic for that base station by selecting from saidresource blocks in accordance with said resource utilisation fractions.